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Steps towards progress
React based in Sweden has produced informative material on AMR for the general public.
Videos are being produced for the general public to generate interest and awareness.
The Irish Department of Health published a National Action Plan on Antimicrobial Resistance in October 2017. The Strategy for the Control of Antimicrobial Resistance in Ireland (SARI), Iaunched in 2001 developed Guidelines for Antimicrobial Stewardship in Hospitals in Ireland in conjunction with the Health Protection Surveillance Centre, these were published in 2009. Following their publication a public information campaign 'Action on Antibiotics' was launched to highlight the need for a change in antibiotic prescribing. Despite this, antibiotic prescribing remains high with variance in adherence to guidelines.
The United Kingdom published a 20-year vision for antimicrobial resistance that sets out the goal of containing and controlling AMR by 2040. The vision is supplemented by a 5-year action plan running from 2019 to 2024, building on the previous action plan (2013–2018).
The World Health Organization has published the 2024 Bacterial Priority Pathogens List which covers 15 families of antibiotic-resistant bacterial pathogens. Notable among these are gram-negative bacteria resistant to last-resort antibiotics, drug-resistant mycobacterium tuberculosis, and other high-burden resistant pathogens such as Salmonella, Shigella, Neisseria gonorrhoeae, Pseudomonas aeruginosa, and Staphylococcus aureus. The inclusion of these pathogens in the list underscores their global impact in terms of burden, as well as issues related to transmissibility, treatability, and prevention options. It also reflects the R&D pipeline of new treatments and emerging resistance trends.
Antibiotic Awareness Week
The World Health Organization has promoted the first World Antibiotic Awareness Week running from 16 to 22 November 2015. The aim of the week is to increase global awareness of antibiotic resistance. It also wants to promote the correct usage of antibiotics across all fields in order to prevent further instances of antibiotic resistance.
World Antibiotic Awareness Week has been held every November since 2015. For 2017, the Food and Agriculture Organization of the United Nations (FAO), the World Health Organization (WHO) and the World Organisation for Animal Health (OIE) are together calling for responsible use of antibiotics in humans and animals to reduce the emergence of antibiotic resistance.
United Nations | Antimicrobial resistance | Wikipedia | 495 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
In 2016 the Secretary-General of the United Nations convened the Interagency Coordination Group (IACG) on Antimicrobial Resistance. The IACG worked with international organizations and experts in human, animal, and plant health to create a plan to fight antimicrobial resistance. Their report released in April 2019 highlights the seriousness of antimicrobial resistance and the threat it poses to world health. It suggests five recommendations for member states to follow in order to tackle this increasing threat. The IACG recommendations are as follows:
Accelerate progress in countries
Innovate to secure the future
Collaborate for more effective action
Invest for a sustainable response
Strengthen accountability and global governance
Mechanisms and organisms
Bacteria | Antimicrobial resistance | Wikipedia | 139 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
The five main mechanisms by which bacteria exhibit resistance to antibiotics are:
Drug inactivation or modification: for example, enzymatic deactivation of penicillin G in some penicillin-resistant bacteria through the production of β-lactamases. Drugs may also be chemically modified through the addition of functional groups by transferase enzymes; for example, acetylation, phosphorylation, or adenylation are common resistance mechanisms to aminoglycosides. Acetylation is the most widely used mechanism and can affect a number of drug classes.
Alteration of target- or binding site: for example, alteration of PBP—the binding target site of penicillins—in MRSA and other penicillin-resistant bacteria. Another protective mechanism found among bacterial species is ribosomal protection proteins. These proteins protect the bacterial cell from antibiotics that target the cell's ribosomes to inhibit protein synthesis. The mechanism involves the binding of the ribosomal protection proteins to the ribosomes of the bacterial cell, which in turn changes its conformational shape. This allows the ribosomes to continue synthesizing proteins essential to the cell while preventing antibiotics from binding to the ribosome to inhibit protein synthesis.
Alteration of metabolic pathway: for example, some sulfonamide-resistant bacteria do not require para-aminobenzoic acid (PABA), an important precursor for the synthesis of folic acid and nucleic acids in bacteria inhibited by sulfonamides, instead, like mammalian cells, they turn to using preformed folic acid.
Reduced drug accumulation: by decreasing drug permeability or increasing active efflux (pumping out) of the drugs across the cell surface These pumps within the cellular membrane of certain bacterial species are used to pump antibiotics out of the cell before they are able to do any damage. They are often activated by a specific substrate associated with an antibiotic, as in fluoroquinolone resistance.
Ribosome splitting and recycling: for example, drug-mediated stalling of the ribosome by lincomycin and erythromycin unstalled by a heat shock protein found in Listeria monocytogenes, which is a homologue of HflX from other bacteria. Liberation of the ribosome from the drug allows further translation and consequent resistance to the drug.
There are several different types of germs that have developed a resistance over time. | Antimicrobial resistance | Wikipedia | 499 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
The six pathogens causing most deaths associated with resistance are Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Streptococcus pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa. They were responsible for 929,000 deaths attributable to resistance and 3.57 million deaths associated with resistance in 2019.
Penicillinase-producing Neisseria gonorrhoeae developed a resistance to penicillin in 1976. Another example is Azithromycin-resistant Neisseria gonorrhoeae, which developed a resistance to azithromycin in 2011.
In gram-negative bacteria, plasmid-mediated resistance genes produce proteins that can bind to DNA gyrase, protecting it from the action of quinolones. Finally, mutations at key sites in DNA gyrase or topoisomerase IV can decrease their binding affinity to quinolones, decreasing the drug's effectiveness. | Antimicrobial resistance | Wikipedia | 214 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
Some bacteria are naturally resistant to certain antibiotics; for example, gram-negative bacteria are resistant to most β-lactam antibiotics due to the presence of β-lactamase. Antibiotic resistance can also be acquired as a result of either genetic mutation or horizontal gene transfer. Although mutations are rare, with spontaneous mutations in the pathogen genome occurring at a rate of about 1 in 105 to 1 in 108 per chromosomal replication, the fact that bacteria reproduce at a high rate allows for the effect to be significant. Given that lifespans and production of new generations can be on a timescale of mere hours, a new (de novo) mutation in a parent cell can quickly become an inherited mutation of widespread prevalence, resulting in the microevolution of a fully resistant colony. However, chromosomal mutations also confer a cost of fitness. For example, a ribosomal mutation may protect a bacterial cell by changing the binding site of an antibiotic but may result in slower growth rate. Moreover, some adaptive mutations can propagate not only through inheritance but also through horizontal gene transfer. The most common mechanism of horizontal gene transfer is the transferring of plasmids carrying antibiotic resistance genes between bacteria of the same or different species via conjugation. However, bacteria can also acquire resistance through transformation, as in Streptococcus pneumoniae uptaking of naked fragments of extracellular DNA that contain antibiotic resistance genes to streptomycin, through transduction, as in the bacteriophage-mediated transfer of tetracycline resistance genes between strains of S. pyogenes, or through gene transfer agents, which are particles produced by the host cell that resemble bacteriophage structures and are capable of transferring DNA.
Antibiotic resistance can be introduced artificially into a microorganism through laboratory protocols, sometimes used as a selectable marker to examine the mechanisms of gene transfer or to identify individuals that absorbed a piece of DNA that included the resistance gene and another gene of interest.
Recent findings show no necessity of large populations of bacteria for the appearance of antibiotic resistance. Small populations of Escherichia coli in an antibiotic gradient can become resistant. Any heterogeneous environment with respect to nutrient and antibiotic gradients may facilitate antibiotic resistance in small bacterial populations. Researchers hypothesize that the mechanism of resistance evolution is based on four SNP mutations in the genome of E. coli produced by the gradient of antibiotic. | Antimicrobial resistance | Wikipedia | 504 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
In one study, which has implications for space microbiology, a non-pathogenic strain E. coli MG1655 was exposed to trace levels of the broad spectrum antibiotic chloramphenicol, under simulated microgravity (LSMMG, or Low Shear Modeled Microgravity) over 1000 generations. The adapted strain acquired resistance to not only chloramphenicol, but also cross-resistance to other antibiotics; this was in contrast to the observation on the same strain, which was adapted to over 1000 generations under LSMMG, but without any antibiotic exposure; the strain in this case did not acquire any such resistance. Thus, irrespective of where they are used, the use of an antibiotic would likely result in persistent resistance to that antibiotic, as well as cross-resistance to other antimicrobials.
In recent years, the emergence and spread of β-lactamases called carbapenemases has become a major health crisis. One such carbapenemase is New Delhi metallo-beta-lactamase 1 (NDM-1), an enzyme that makes bacteria resistant to a broad range of beta-lactam antibiotics. The most common bacteria that make this enzyme are gram-negative such as E. coli and Klebsiella pneumoniae, but the gene for NDM-1 can spread from one strain of bacteria to another by horizontal gene transfer.
Viruses
Specific antiviral drugs are used to treat some viral infections. These drugs prevent viruses from reproducing by inhibiting essential stages of the virus's replication cycle in infected cells. Antivirals are used to treat HIV, hepatitis B, hepatitis C, influenza, herpes viruses including varicella zoster virus, cytomegalovirus and Epstein–Barr virus. With each virus, some strains have become resistant to the administered drugs.
Antiviral drugs typically target key components of viral reproduction; for example, oseltamivir targets influenza neuraminidase, while guanosine analogs inhibit viral DNA polymerase. Resistance to antivirals is thus acquired through mutations in the genes that encode the protein targets of the drugs. | Antimicrobial resistance | Wikipedia | 448 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
Resistance to HIV antivirals is problematic, and even multi-drug resistant strains have evolved. One source of resistance is that many current HIV drugs, including NRTIs and NNRTIs, target reverse transcriptase; however, HIV-1 reverse transcriptase is highly error prone and thus mutations conferring resistance arise rapidly. Resistant strains of the HIV virus emerge rapidly if only one antiviral drug is used. Using three or more drugs together, termed combination therapy, has helped to control this problem, but new drugs are needed because of the continuing emergence of drug-resistant HIV strains.
Fungi
Infections by fungi are a cause of high morbidity and mortality in immunocompromised persons, such as those with HIV/AIDS, tuberculosis or receiving chemotherapy. The fungi Candida, Cryptococcus neoformans and Aspergillus fumigatus cause most of these infections and antifungal resistance occurs in all of them. Multidrug resistance in fungi is increasing because of the widespread use of antifungal drugs to treat infections in immunocompromised individuals and the use of some agricultural antifungals. Antifungal resistant disease is associated with increased mortality.
Some fungi (e.g. Candida krusei and fluconazole) exhibit intrinsic resistance to certain antifungal drugs or classes, whereas some species develop antifungal resistance to external pressures. Antifungal resistance is a One Health concern, driven by multiple extrinsic factors, including extensive fungicidal use, overuse of clinical antifungals, environmental change and host factors.
In the USA fluconazole-resistant Candida species and azole resistance in Aspergillus fumigatus have been highlighted as a growing threat.
More than 20 species of Candida can cause candidiasis infection, the most common of which is Candida albicans. Candida yeasts normally inhabit the skin and mucous membranes without causing infection. However, overgrowth of Candida can lead to candidiasis. Some Candida species (e.g. Candida glabrata) are becoming resistant to first-line and second-line antifungal agents such as echinocandins and azoles. | Antimicrobial resistance | Wikipedia | 461 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
The emergence of Candida auris as a potential human pathogen that sometimes exhibits multi-class antifungal drug resistance is concerning and has been associated with several outbreaks globally. The WHO has released a priority fungal pathogen list, including pathogens with antifungal resistance.
The identification of antifungal resistance is undermined by limited classical diagnosis of infection, where a culture is lacking, preventing susceptibility testing. National and international surveillance schemes for fungal disease and antifungal resistance are limited, hampering the understanding of the disease burden and associated resistance. The application of molecular testing to identify genetic markers associating with resistance may improve the identification of antifungal resistance, but the diversity of mutations associated with resistance is increasing across the fungal species causing infection. In addition, a number of resistance mechanisms depend on up-regulation of selected genes (for instance reflux pumps) rather than defined mutations that are amenable to molecular detection.
Due to the limited number of antifungals in clinical use and the increasing global incidence of antifungal resistance, using the existing antifungals in combination might be beneficial in some cases but further research is needed. Similarly, other approaches that might help to combat the emergence of antifungal resistance could rely on the development of host-directed therapies such as immunotherapy or vaccines.
Parasites
The protozoan parasites that cause the diseases malaria, trypanosomiasis, toxoplasmosis, cryptosporidiosis and leishmaniasis are important human pathogens.
Malarial parasites that are resistant to the drugs that are currently available to infections are common and this has led to increased efforts to develop new drugs. Resistance to recently developed drugs such as artemisinin has also been reported. The problem of drug resistance in malaria has driven efforts to develop vaccines.
Trypanosomes are parasitic protozoa that cause African trypanosomiasis and Chagas disease (American trypanosomiasis). There are no vaccines to prevent these infections so drugs such as pentamidine and suramin, benznidazole and nifurtimox are used to treat infections. These drugs are effective but infections caused by resistant parasites have been reported.
Leishmaniasis is caused by protozoa and is an important public health problem worldwide, especially in sub-tropical and tropical countries. Drug resistance has "become a major concern".
Global and genomic data | Antimicrobial resistance | Wikipedia | 503 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
In 2022, genomic epidemiologists reported results from a global survey of antimicrobial resistance via genomic wastewater-based epidemiology, finding large regional variations, providing maps, and suggesting resistance genes are also passed on between microbial species that are not closely related. The WHO provides the Global Antimicrobial Resistance and Use Surveillance System (GLASS) reports which summarize annual (e.g. 2020's) data on international AMR, also including an interactive dashboard.
Epidemiology
United Kingdom
Public Health England reported that the total number of antibiotic resistant infections in England rose by 9% from 55,812 in 2017 to 60,788 in 2018, but antibiotic consumption had fallen by 9% from 20.0 to 18.2 defined daily doses per 1,000 inhabitants per day between 2014 and 2018.
United States
The Centers for Disease Control and Prevention reported that more than 2.8 million cases of antibiotic resistance have been reported. However, in 2019 overall deaths from antibiotic-resistant infections decreased by 18% and deaths in hospitals decreased by 30%.
The COVID pandemic caused a reversal of much of the progress made on attenuating the effects of antibiotic resistance, resulting in more antibiotic use, more resistant infections, and less data on preventive action. Hospital-onset infections and deaths both increased by 15% in 2020, and significantly higher rates of infections were reported for 4 out of 6 types of healthcare associated infections.
History
The 1950s to 1970s represented the golden age of antibiotic discovery, where countless new classes of antibiotics were discovered to treat previously incurable diseases such as tuberculosis and syphilis. However, since that time the discovery of new classes of antibiotics has been almost nonexistent, and represents a situation that is especially problematic considering the resiliency of bacteria shown over time and the continued misuse and overuse of antibiotics in treatment. | Antimicrobial resistance | Wikipedia | 391 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
The phenomenon of antimicrobial resistance caused by overuse of antibiotics was predicted as early as 1945 by Alexander Fleming who said "The time may come when penicillin can be bought by anyone in the shops. Then there is the danger that the ignorant man may easily under-dose himself and by exposing his microbes to nonlethal quantities of the drug make them resistant." Without the creation of new and stronger antibiotics an era where common infections and minor injuries can kill, and where complex procedures such as surgery and chemotherapy become too risky, is a very real possibility. Antimicrobial resistance can lead to epidemics of enormous proportions if preventive actions are not taken. In this day and age current antimicrobial resistance leads to longer hospital stays, higher medical costs, and increased mortality.
Society and culture
Innovation policy
Since the mid-1980s pharmaceutical companies have invested in medications for cancer or chronic disease that have greater potential to make money and have "de-emphasized or dropped development of antibiotics". On 20 January 2016 at the World Economic Forum in Davos, Switzerland, more than "80 pharmaceutical and diagnostic companies" from around the world called for "transformational commercial models" at a global level to spur research and development on antibiotics and on the "enhanced use of diagnostic tests that can rapidly identify the infecting organism". A number of countries are considering or implementing delinked payment models for new antimicrobials whereby payment is based on value rather than volume of drug sales. This offers the opportunity to pay for valuable new drugs even if they are reserved for use in relatively rare drug resistant infections.
Legal frameworks
Some global health scholars have argued that a global, legal framework is needed to prevent and control antimicrobial resistance. For instance, binding global policies could be used to create antimicrobial use standards, regulate antibiotic marketing, and strengthen global surveillance systems. Ensuring compliance of involved parties is a challenge. Global antimicrobial resistance policies could take lessons from the environmental sector by adopting strategies that have made international environmental agreements successful in the past such as: sanctions for non-compliance, assistance for implementation, majority vote decision-making rules, an independent scientific panel, and specific commitments.
United States | Antimicrobial resistance | Wikipedia | 449 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
For the United States 2016 budget, U.S. president Barack Obama proposed to nearly double the amount of federal funding to "combat and prevent" antibiotic resistance to more than $1.2 billion. Many international funding agencies like USAID, DFID, SIDA and Bill & Melinda Gates Foundation have pledged money for developing strategies to counter antimicrobial resistance.
On 27 March 2015, the White House released a comprehensive plan to address the increasing need for agencies to combat the rise of antibiotic-resistant bacteria. The Task Force for Combating Antibiotic-Resistant Bacteria developed The National Action Plan for Combating Antibiotic-Resistant Bacteria with the intent of providing a roadmap to guide the US in the antibiotic resistance challenge and with hopes of saving many lives. This plan outlines steps taken by the Federal government over the next five years needed in order to prevent and contain outbreaks of antibiotic-resistant infections; maintain the efficacy of antibiotics already on the market; and to help to develop future diagnostics, antibiotics, and vaccines.
The Action Plan was developed around five goals with focuses on strengthening health care, public health veterinary medicine, agriculture, food safety and research, and manufacturing. These goals, as listed by the White House, are as follows:
Slow the Emergence of Resistant Bacteria and Prevent the Spread of Resistant Infections
Strengthen National One-Health Surveillance Efforts to Combat Resistance
Advance Development and use of Rapid and Innovative Diagnostic Tests for Identification and Characterization of Resistant Bacteria
Accelerate Basic and Applied Research and Development for New Antibiotics, Other Therapeutics, and Vaccines
Improve International Collaboration and Capacities for Antibiotic Resistance Prevention, Surveillance, Control and Antibiotic Research and Development
The following are goals set to meet by 2020:
Establishment of antimicrobial programs within acute care hospital settings
Reduction of inappropriate antibiotic prescription and use by at least 50% in outpatient settings and 20% inpatient settings
Establishment of State Antibiotic Resistance (AR) Prevention Programs in all 50 states
Elimination of the use of medically important antibiotics for growth promotion in food-producing animals.
Current Status of AMR in the U.S. | Antimicrobial resistance | Wikipedia | 420 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
As of 2023, antimicrobial resistance (AMR) remains a significant public health threat in the United States. According to the Centers for Disease Control and Prevention's 2023 Report on Antibiotic Resistance Threats, over 2.8 million antibiotic-resistant infections occur in the U.S. each year, leading to at least 35,000 deaths annually. Among the most concerning resistant pathogens are Carbapenem-resistant Enterobacteriaceae (CRE), Methicillin-resistant Staphylococcus aureus (MRSA), and Clostridioides difficile (C. diff), all of which continue to be responsible for severe healthcare-associated infections (HAIs).
The COVID-19 pandemic led to a significant disruption in healthcare, with an increase in the use of antibiotics during the treatment of viral infections. This rise in antibiotic prescribing, coupled with overwhelmed healthcare systems, contributed to a resurgence in AMR during the pandemic years. A 2021 CDC report identified a sharp increase in HAIs caused by resistant pathogens in COVID-19 patients, a trend that has persisted into 2023. Recent data suggest that although antibiotic use has decreased since the pandemic, some resistant pathogens remain prevalent in healthcare settings.
The CDC has also expanded its Get Ahead of Sepsis campaign in 2023, focusing on raising awareness of AMR's role in sepsis and promoting the judicious use of antibiotics in both healthcare and community settings. This initiative has reached millions through social media, healthcare facilities, and public health outreach, aiming to educate the public on the importance of preventing infections and reducing antibiotic misuse.
Policies
According to World Health Organization, policymakers can help tackle resistance by strengthening resistance-tracking and laboratory capacity and by regulating and promoting the appropriate use of medicines. Policymakers and industry can help tackle resistance by: fostering innovation and research and development of new tools; and promoting cooperation and information sharing among all stakeholders. | Antimicrobial resistance | Wikipedia | 414 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
The U.S. government continues to prioritize AMR mitigation through policy and legislation. In 2023, the National Action Plan for Combating Antibiotic-Resistant Bacteria (CARB) 2023-2028 was released, outlining strategic objectives for reducing antibiotic-resistant infections, advancing infection prevention, and accelerating research on new antibiotics. The plan also emphasizes the importance of improving antibiotic stewardship across healthcare, agriculture, and veterinary settings.
Furthermore, the PASTEUR Act (Pioneering Antimicrobial Subscriptions to End Upsurging Resistance) has gained momentum in Congress. If passed, the bill would create a subscription-based payment model to incentivize the development of new antimicrobial drugs, while supporting antimicrobial stewardship programs to reduce the misuse of existing antibiotics. This legislation is considered a critical step toward addressing the economic barriers to developing new antimicrobials.
Policy evaluation
Measuring the costs and benefits of strategies to combat AMR is difficult and policies may only have effects in the distant future. In other infectious diseases this problem has been addressed by using mathematical models. More research is needed to understand how AMR develops and spreads so that mathematical modelling can be used to anticipate the likely effects of different policies.
Further research
Rapid testing and diagnostics
Distinguishing infections requiring antibiotics from self-limiting ones is clinically challenging. In order to guide appropriate use of antibiotics and prevent the evolution and spread of antimicrobial resistance, diagnostic tests that provide clinicians with timely, actionable results are needed.
Acute febrile illness is a common reason for seeking medical care worldwide and a major cause of morbidity and mortality. In areas with decreasing malaria incidence, many febrile patients are inappropriately treated for malaria, and in the absence of a simple diagnostic test to identify alternative causes of fever, clinicians presume that a non-malarial febrile illness is most likely a bacterial infection, leading to inappropriate use of antibiotics. Multiple studies have shown that the use of malaria rapid diagnostic tests without reliable tools to distinguish other fever causes has resulted in increased antibiotic use. | Antimicrobial resistance | Wikipedia | 430 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
Antimicrobial susceptibility testing (AST) can facilitate a precision medicine approach to treatment by helping clinicians to prescribe more effective and targeted antimicrobial therapy. At the same time with traditional phenotypic AST it can take 12 to 48 hours to obtain a result due to the time taken for organisms to grow on/in culture media. Rapid testing, possible from molecular diagnostics innovations, is defined as "being feasible within an 8-h working shift". There are several commercial Food and Drug Administration-approved assays available which can detect AMR genes from a variety of specimen types. Progress has been slow due to a range of reasons including cost and regulation. Genotypic AMR characterisation methods are, however, being increasingly used in combination with machine learning algorithms in research to help better predict phenotypic AMR from organism genotype.
Optical techniques such as phase contrast microscopy in combination with single-cell analysis are another powerful method to monitor bacterial growth. In 2017, scientists from Uppsala University in Sweden published a method that applies principles of microfluidics and cell tracking, to monitor bacterial response to antibiotics in less than 30 minutes overall manipulation time. This invention was awarded the 8M£ Longitude Prize on AMR in 2024. Recently, this platform has been advanced by coupling microfluidic chip with optical tweezing in order to isolate bacteria with altered phenotype directly from the analytical matrix.
Rapid diagnostic methods have also been trialled as antimicrobial stewardship interventions to influence the healthcare drivers of AMR. Serum procalcitonin measurement has been shown to reduce mortality rate, antimicrobial consumption and antimicrobial-related side-effects in patients with respiratory infections, but impact on AMR has not yet been demonstrated. Similarly, point of care serum testing of the inflammatory biomarker C-reactive protein has been shown to influence antimicrobial prescribing rates in this patient cohort, but further research is required to demonstrate an effect on rates of AMR. Clinical investigation to rule out bacterial infections are often done for patients with pediatric acute respiratory infections. Currently it is unclear if rapid viral testing affects antibiotic use in children. | Antimicrobial resistance | Wikipedia | 450 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
Vaccines
Vaccines are an essential part of the response to reduce AMR as they prevent infections, reduce the use and overuse of antimicrobials, and slow the emergence and spread of drug-resistant pathogens.
Microorganisms usually do not develop resistance to vaccines because vaccines reduce the spread of the infection and target the pathogen in multiple ways in the same host and possibly in different ways between different hosts. Furthermore, if the use of vaccines increases, there is evidence that antibiotic resistant strains of pathogens will decrease; the need for antibiotics will naturally decrease as vaccines prevent infection before it occurs. A 2024 report by WHO finds that vaccines against 24 pathogens could reduce the number of antibiotics needed by 22% or 2.5 billion defined daily doses globally every year. If vaccines could be rolled out against all the evaluated pathogens, they could save a third of the hospital costs associated with AMR. Vaccinated people have fewer infections and are protected against potential complications from secondary infections that may need antimicrobial medicines or require admission to hospital. However, there are well documented cases of vaccine resistance, although these are usually much less of a problem than antimicrobial resistance.
While theoretically promising, antistaphylococcal vaccines have shown limited efficacy, because of immunological variation between Staphylococcus species, and the limited duration of effectiveness of the antibodies produced. Development and testing of more effective vaccines is underway.
Two registrational trials have evaluated vaccine candidates in active immunization strategies against S. aureus infection. In a phase II trial, a bivalent vaccine of capsular proteins 5 & 8 was tested in 1804 hemodialysis patients with a primary fistula or synthetic graft vascular access. After 40 weeks following vaccination a protective effect was seen against S. aureus bacteremia, but not at 54 weeks following vaccination. Based on these results, a second trial was conducted which failed to show efficacy.
Merck tested V710, a vaccine targeting IsdB, in a blinded randomized trial in patients undergoing median sternotomy. The trial was terminated after a higher rate of multiorgan system failure–related deaths was found in the V710 recipients. Vaccine recipients who developed S. aureus infection were five times more likely to die than control recipients who developed S. aureus infection. | Antimicrobial resistance | Wikipedia | 478 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
Numerous investigators have suggested that a multiple-antigen vaccine would be more effective, but a lack of biomarkers defining human protective immunity keep these proposals in the logical, but strictly hypothetical arena.
Antibody therapy
Antibodies are promising against antimicrobial resistance. Monoclonal antibodies (mAbs) target bacterial virulence factors, aiding in bacterial destruction through various mechanisms. Three FDA-approved antibodies target B. anthracis and C. difficile toxins. Innovative strategies include DSTA4637S, an antibody-antibiotic conjugate, and MEDI13902, a bispecific antibody targeting Pseudomonas aeruginosa components.
Alternating therapy
Alternating therapy is a proposed method in which two or three antibiotics are taken in a rotation versus taking just one antibiotic such that bacteria resistant to one antibiotic are killed when the next antibiotic is taken. Studies have found that this method reduces the rate at which antibiotic resistant bacteria emerge in vitro relative to a single drug for the entire duration.
Studies have found that bacteria that evolve antibiotic resistance towards one group of antibiotic may become more sensitive to others. This phenomenon can be used to select against resistant bacteria using an approach termed collateral sensitivity cycling, which has recently been found to be relevant in developing treatment strategies for chronic infections caused by Pseudomonas aeruginosa. Despite its promise, large-scale clinical and experimental studies revealed limited evidence of susceptibility to antibiotic cycling across various pathogens.
Development of new drugs
Since the discovery of antibiotics, research and development (R&D) efforts have provided new drugs in time to treat bacteria that became resistant to older antibiotics, but in the 2000s there has been concern that development has slowed enough that seriously ill people may run out of treatment options. Another concern is that practitioners may become reluctant to perform routine surgeries because of the increased risk of harmful infection. Backup treatments can have serious side-effects; for example, antibiotics like aminoglycosides (such as amikacin, gentamicin, kanamycin, streptomycin, etc.) used for the treatment of drug-resistant tuberculosis and cystic fibrosis can cause respiratory disorders, deafness and kidney failure. | Antimicrobial resistance | Wikipedia | 451 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
The potential crisis at hand is the result of a marked decrease in industry research and development. Poor financial investment in antibiotic research has exacerbated the situation. The pharmaceutical industry has little incentive to invest in antibiotics because of the high risk and because the potential financial returns are less likely to cover the cost of development than for other pharmaceuticals. In 2011, Pfizer, one of the last major pharmaceutical companies developing new antibiotics, shut down its primary research effort, citing poor shareholder returns relative to drugs for chronic illnesses. However, small and medium-sized pharmaceutical companies are still active in antibiotic drug research. In particular, apart from classical synthetic chemistry methodologies, researchers have developed a combinatorial synthetic biology platform on single cell level in a high-throughput screening manner to diversify novel lanthipeptides.
In the 5–10 years since 2010, there has been a significant change in the ways new antimicrobial agents are discovered and developed – principally via the formation of public-private funding initiatives. These include CARB-X, which focuses on nonclinical and early phase development of novel antibiotics, vaccines, rapid diagnostics; Novel Gram Negative Antibiotic (GNA-NOW), which is part of the EU's Innovative Medicines Initiative; and Replenishing and Enabling the Pipeline for Anti-infective Resistance Impact Fund (REPAIR). Later stage clinical development is supported by the AMR Action Fund, which in turn is supported by multiple investors with the aim of developing 2–4 new antimicrobial agents by 2030. The delivery of these trials is facilitated by national and international networks supported by the Clinical Research Network of the National Institute for Health and Care Research (NIHR), European Clinical Research Alliance in Infectious Diseases (ECRAID) and the recently formed ADVANCE-ID, which is a clinical research network based in Asia. The Global Antibiotic Research and Development Partnership (GARDP) is generating new evidence for global AMR threats such as neonatal sepsis, treatment of serious bacterial infections and sexually transmitted infections as well as addressing global access to new and strategically important antibacterial drugs. | Antimicrobial resistance | Wikipedia | 434 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
The discovery and development of new antimicrobial agents has been facilitated by regulatory advances, which have been principally led by the European Medicines Agency (EMA) and the Food and Drug Administration (FDA). These processes are increasingly aligned although important differences remain and drug developers must prepare separate documents. New development pathways have been developed to help with the approval of new antimicrobial agents that address unmet needs such as the Limited Population Pathway for Antibacterial and Antifungal Drugs (LPAD). These new pathways are required because of difficulties in conducting large definitive phase III clinical trials in a timely way.
Some of the economic impediments to the development of new antimicrobial agents have been addressed by innovative reimbursement schemes that delink payment of antimicrobials from volume-based sales. In the UK, a market entry reward scheme has been pioneered by the National Institute for Clinical Excellence (NICE) whereby an annual subscription fee is paid for use of strategically valuable antimicrobial agents – cefiderocol and ceftazidime-aviabactam are the first agents to be used in this manner and the scheme is potential blueprint for comparable programs in other countries.
The available classes of antifungal drugs are still limited but as of 2021 novel classes of antifungals are being developed and are undergoing various stages of clinical trials to assess performance.
Scientists have started using advanced computational approaches with supercomputers for the development of new antibiotic derivatives to deal with antimicrobial resistance.
Biomaterials
Using antibiotic-free alternatives in bone infection treatment may help decrease the use of antibiotics and thus antimicrobial resistance. The bone regeneration material bioactive glass S53P4 has shown to effectively inhibit the bacterial growth of up to 50 clinically relevant bacteria including MRSA and MRSE.
Nanomaterials | Antimicrobial resistance | Wikipedia | 383 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
During the last decades, copper and silver nanomaterials have demonstrated appealing features for the development of a new family of antimicrobial agents. Nanoparticles (1–100 nm) show unique properties and promise as antimicrobial agents against resistant bacteria. Silver (AgNPs) and gold nanoparticles (AuNPs) are extensively studied, disrupting bacterial cell membranes and interfering with protein synthesis. Zinc oxide (ZnO NPs), copper (CuNPs), and silica (SiNPs) nanoparticles also exhibit antimicrobial properties. However, high synthesis costs, potential toxicity, and instability pose challenges. To overcome these, biological synthesis methods and combination therapies with other antimicrobials are explored. Enhanced biocompatibility and targeting are also under investigation to improve efficacy.
Rediscovery of ancient treatments
Similar to the situation in malaria therapy, where successful treatments based on ancient recipes have been found, there has already been some success in finding and testing ancient drugs and other treatments that are effective against AMR bacteria.
Computational community surveillance
One of the key tools identified by the WHO and others for the fight against rising antimicrobial resistance is improved surveillance of the spread and movement of AMR genes through different communities and regions. Recent advances in high-throughput DNA sequencing as a result of the Human Genome Project have resulted in the ability to determine the individual microbial genes in a sample. Along with the availability of databases of known antimicrobial resistance genes, such as the Comprehensive Antimicrobial Resistance Database (CARD) and ResFinder, this allows the identification of all the antimicrobial resistance genes within the sample – the so-called "resistome". In doing so, a profile of these genes within a community or environment can be determined, providing insights into how antimicrobial resistance is spreading through a population and allowing for the identification of resistance that is of concern.
Phage therapy
Phage therapy is the therapeutic use of bacteriophages to treat pathogenic bacterial infections. Phage therapy has many potential applications in human medicine as well as dentistry, veterinary science, and agriculture. | Antimicrobial resistance | Wikipedia | 443 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
Phage therapy relies on the use of naturally occurring bacteriophages to infect and lyse bacteria at the site of infection in a host. Due to current advances in genetics and biotechnology these bacteriophages can possibly be manufactured to treat specific infections. Phages can be bioengineered to target multidrug-resistant bacterial infections, and their use involves the added benefit of preventing the elimination of beneficial bacteria in the human body. Phages destroy bacterial cell walls and membrane through the use of lytic proteins which kill bacteria by making many holes from the inside out. Bacteriophages can even possess the ability to digest the biofilm that many bacteria develop that protect them from antibiotics in order to effectively infect and kill bacteria. Bioengineering can play a role in creating successful bacteriophages.
Understanding the mutual interactions and evolutions of bacterial and phage populations in the environment of a human or animal body is essential for rational phage therapy.
Bacteriophagics are used against antibiotic resistant bacteria in Georgia (George Eliava Institute) and in one institute in Wrocław, Poland. Bacteriophage cocktails are common drugs sold over the counter in pharmacies in eastern countries. In Belgium, four patients with severe musculoskeletal infections received bacteriophage therapy with concomitant antibiotics. After a single course of phage therapy, no recurrence of infection occurred and no severe side-effects related to the therapy were detected. | Antimicrobial resistance | Wikipedia | 308 | 1914 | https://en.wikipedia.org/wiki/Antimicrobial%20resistance | Biology and health sciences | Anti-infectives | Health |
In immunology, an antigen (Ag) is a molecule, moiety, foreign particulate matter, or an allergen, such as pollen, that can bind to a specific antibody or T-cell receptor. The presence of antigens in the body may trigger an immune response.
Antigens can be proteins, peptides (amino acid chains), polysaccharides (chains of simple sugars), lipids, or nucleic acids. Antigens exist on normal cells, cancer cells, parasites, viruses, fungi, and bacteria.
Antigens are recognized by antigen receptors, including antibodies and T-cell receptors. Diverse antigen receptors are made by cells of the immune system so that each cell has a specificity for a single antigen. Upon exposure to an antigen, only the lymphocytes that recognize that antigen are activated and expanded, a process known as clonal selection. In most cases, antibodies are antigen-specific, meaning that an antibody can only react to and bind one specific antigen; in some instances, however, antibodies may cross-react to bind more than one antigen. The reaction between an antigen and an antibody is called the antigen-antibody reaction.
Antigen can originate either from within the body ("self-protein" or "self antigens") or from the external environment ("non-self"). The immune system identifies and attacks "non-self" external antigens. Antibodies usually do not react with self-antigens due to negative selection of T cells in the thymus and B cells in the bone marrow. The diseases in which antibodies react with self antigens and damage the body's own cells are called autoimmune diseases.
Vaccines are examples of antigens in an immunogenic form, which are intentionally administered to a recipient to induce the memory function of the adaptive immune system towards antigens of the pathogen invading that recipient. The vaccine for seasonal influenza is a common example. | Antigen | Wikipedia | 394 | 1915 | https://en.wikipedia.org/wiki/Antigen | Biology and health sciences | Immune system | Biology |
Etymology
Paul Ehrlich coined the term antibody () in his side-chain theory at the end of the 19th century. In 1899, Ladislas Deutsch (László Detre) named the hypothetical substances halfway between bacterial constituents and antibodies "antigenic or immunogenic substances" (). He originally believed those substances to be precursors of antibodies, just as a zymogen is a precursor of an enzyme. But, by 1903, he understood that an antigen induces the production of immune bodies (antibodies) and wrote that the word antigen is a contraction of antisomatogen (). The Oxford English Dictionary indicates that the logical construction should be "anti(body)-gen".
The term originally referred to a substance that acts as an antibody generator. | Antigen | Wikipedia | 157 | 1915 | https://en.wikipedia.org/wiki/Antigen | Biology and health sciences | Immune system | Biology |
Terminology
Epitope – the distinct surface features of an antigen, its antigenic determinant.Antigenic molecules, normally "large" biological polymers, usually present surface features that can act as points of interaction for specific antibodies. Any such feature constitutes an epitope. Most antigens have the potential to be bound by multiple antibodies, each of which is specific to one of the antigen's epitopes. Using the "lock and key" metaphor, the antigen can be seen as a string of keys (epitopes) each of which matches a different lock (antibody). Different antibody idiotypes, each have distinctly formed complementarity-determining regions.
Allergen – A substance capable of causing an allergic reaction. The (detrimental) reaction may result after exposure via ingestion, inhalation, injection, or contact with skin.
Superantigen – A class of antigens that cause non-specific activation of T-cells, resulting in polyclonal T-cell activation and massive cytokine release.
Tolerogen – A substance that invokes a specific immune non-responsiveness due to its molecular form. If its molecular form is changed, a tolerogen can become an immunogen.
Immunoglobulin-binding protein – Proteins such as protein A, protein G, and protein L that are capable of binding to antibodies at positions outside of the antigen-binding site. While antigens are the "target" of antibodies, immunoglobulin-binding proteins "attack" antibodies.
T-dependent antigen – Antigens that require the assistance of T cells to induce the formation of specific antibodies.
T-independent antigen – Antigens that stimulate B cells directly.
Immunodominant antigens – Antigens that dominate (over all others from a pathogen) in their ability to produce an immune response. T cell responses typically are directed against a relatively few immunodominant epitopes, although in some cases (e.g., infection with the malaria pathogen Plasmodium spp.) it is dispersed over a relatively large number of parasite antigens. | Antigen | Wikipedia | 433 | 1915 | https://en.wikipedia.org/wiki/Antigen | Biology and health sciences | Immune system | Biology |
Antigen-presenting cells present antigens in the form of peptides on histocompatibility molecules. The T cells selectively recognize the antigens; depending on the antigen and the type of the histocompatibility molecule, different types of T cells will be activated. For T-cell receptor (TCR) recognition, the peptide must be processed into small fragments inside the cell and presented by a major histocompatibility complex (MHC). The antigen cannot elicit the immune response without the help of an immunologic adjuvant. Similarly, the adjuvant component of vaccines plays an essential role in the activation of the innate immune system.
An immunogen is an antigen substance (or adduct) that is able to trigger a humoral (innate) or cell-mediated immune response. It first initiates an innate immune response, which then causes the activation of the adaptive immune response. An antigen binds the highly variable immunoreceptor products (B-cell receptor or T-cell receptor) once these have been generated. Immunogens are those antigens, termed immunogenic, capable of inducing an immune response.
At the molecular level, an antigen can be characterized by its ability to bind to an antibody's paratopes. Different antibodies have the potential to discriminate among specific epitopes present on the antigen surface. A hapten is a small molecule that can only induce an immune response when attached to a larger carrier molecule, such as a protein. Antigens can be proteins, polysaccharides, lipids, nucleic acids or other biomolecules. This includes parts (coats, capsules, cell walls, flagella, fimbriae, and toxins) of bacteria, viruses, and other microorganisms. Non-microbial non-self antigens can include pollen, egg white, and proteins from transplanted tissues and organs or on the surface of transfused blood cells.
Sources
Antigens can be classified according to their source. | Antigen | Wikipedia | 420 | 1915 | https://en.wikipedia.org/wiki/Antigen | Biology and health sciences | Immune system | Biology |
Exogenous antigens
Exogenous antigens are antigens that have entered the body from the outside, for example, by inhalation, ingestion or injection. The immune system's response to exogenous antigens is often subclinical. By endocytosis or phagocytosis, exogenous antigens are taken into the antigen-presenting cells (APCs) and processed into fragments. APCs then present the fragments to T helper cells (CD4+) by the use of class II histocompatibility molecules on their surface. Some T cells are specific for the peptide:MHC complex. They become activated and start to secrete cytokines, substances that activate cytotoxic T lymphocytes (CTL), antibody-secreting B cells, macrophages and other particles.
Some antigens start out as exogenous and later become endogenous (for example, intracellular viruses). Intracellular antigens can be returned to circulation upon the destruction of the infected cell.
Endogenous antigens
Endogenous antigens are generated within normal cells as a result of normal cell metabolism, or because of viral or intracellular bacterial infection. The fragments are then presented on the cell surface in the complex with MHC class I molecules. If activated cytotoxic CD8+ T cells recognize them, the T cells secrete various toxins that cause the lysis or apoptosis of the infected cell. In order to keep the cytotoxic cells from killing cells just for presenting self-proteins, the cytotoxic cells (self-reactive T cells) are deleted as a result of tolerance (negative selection). Endogenous antigens include xenogenic (heterologous), autologous and idiotypic or allogenic (homologous) antigens. Sometimes antigens are part of the host itself in an autoimmune disease.
Autoantigens
An autoantigen is usually a self-protein or protein complex (and sometimes DNA or RNA) that is recognized by the immune system of patients with a specific autoimmune disease. Under normal conditions, these self-proteins should not be the target of the immune system, but in autoimmune diseases, their associated T cells are not deleted and instead attack. | Antigen | Wikipedia | 484 | 1915 | https://en.wikipedia.org/wiki/Antigen | Biology and health sciences | Immune system | Biology |
Neoantigens
Neoantigens are those that are entirely absent from the normal human genome. As compared with nonmutated self-proteins, neoantigens are of relevance to tumor control, as the quality of the T cell pool that is available for these antigens is not affected by central T cell tolerance. Technology to systematically analyze T cell reactivity against neoantigens became available only recently. Neoantigens can be directly detected and quantified.
Viral antigens
For virus-associated tumors, such as cervical cancer and a subset of head and neck cancers, epitopes derived from viral open reading frames contribute to the pool of neoantigens.
Tumor antigens
Tumor antigens are those antigens that are presented by MHC class I or MHC class II molecules on the surface of tumor cells. Antigens found only on such cells are called tumor-specific antigens (TSAs) and generally result from a tumor-specific mutation. More common are antigens that are presented by tumor cells and normal cells, called tumor-associated antigens (TAAs). Cytotoxic T lymphocytes that recognize these antigens may be able to destroy tumor cells.
Tumor antigens can appear on the surface of the tumor in the form of, for example, a mutated receptor, in which case they are recognized by B cells.
For human tumors without a viral etiology, novel peptides (neo-epitopes) are created by tumor-specific DNA alterations.
Process
A large fraction of human tumor mutations are effectively patient-specific. Therefore, neoantigens may also be based on individual tumor genomes. Deep-sequencing technologies can identify mutations within the protein-coding part of the genome (the exome) and predict potential neoantigens. In mice models, for all novel protein sequences, potential MHC-binding peptides were predicted. The resulting set of potential neoantigens was used to assess T cell reactivity. Exome–based analyses were exploited in a clinical setting, to assess reactivity in patients treated by either tumor-infiltrating lymphocyte (TIL) cell therapy or checkpoint blockade. Neoantigen identification was successful for multiple experimental model systems and human malignancies. | Antigen | Wikipedia | 462 | 1915 | https://en.wikipedia.org/wiki/Antigen | Biology and health sciences | Immune system | Biology |
The false-negative rate of cancer exome sequencing is low—i.e.: the majority of neoantigens occur within exonic sequence with sufficient coverage. However, the vast majority of mutations within expressed genes do not produce neoantigens that are recognized by autologous T cells.
As of 2015 mass spectrometry resolution is insufficient to exclude many false positives from the pool of peptides that may be presented by MHC molecules. Instead, algorithms are used to identify the most likely candidates. These algorithms consider factors such as the likelihood of proteasomal processing, transport into the endoplasmic reticulum, affinity for the relevant MHC class I alleles and gene expression or protein translation levels.
The majority of human neoantigens identified in unbiased screens display a high predicted MHC binding affinity. Minor histocompatibility antigens, a conceptually similar antigen class are also correctly identified by MHC binding algorithms. Another potential filter examines whether the mutation is expected to improve MHC binding. The nature of the central TCR-exposed residues of MHC-bound peptides is associated with peptide immunogenicity.
Nativity
A native antigen is an antigen that is not yet processed by an APC to smaller parts. T cells cannot bind native antigens, but require that they be processed by APCs, whereas B cells can be activated by native ones.
Antigenic specificity
Antigenic specificity is the ability of the host cells to recognize an antigen specifically as a unique molecular entity and distinguish it from another with exquisite precision. Antigen specificity is due primarily to the side-chain conformations of the antigen. It is measurable and need not be linear or of a rate-limited step or equation. Both T cells and B cells are cellular components of adaptive immunity. | Antigen | Wikipedia | 370 | 1915 | https://en.wikipedia.org/wiki/Antigen | Biology and health sciences | Immune system | Biology |
Argo Navis (the Ship Argo), or simply Argo, is one of Ptolemy's 48 constellations, now a grouping of three IAU constellations. It is formerly a single large constellation in the southern sky. The genitive is "Argus Navis", abbreviated "Arg". John Flamsteed and other early modern astronomers called it Navis (the Ship), genitive "Navis", abbreviated "Nav".
The constellation proved to be of unwieldy size, as it was 28% larger than the next largest constellation and had more than 160 easily visible stars. The 1755 catalogue of Nicolas Louis de Lacaille divided it into the three modern constellations that occupy much of the same area: Carina (the keel), Puppis (the poop deck or stern), and Vela (the sails).
Argo derived from the ship Argo in Greek mythology, sailed by Jason and the Argonauts to Colchis in search of the Golden Fleece. Some stars of Puppis and Vela can be seen from Mediterranean latitudes in winter and spring, the ship appearing to skim along the "river of the Milky Way." The precession of the equinoxes has caused the position of the stars from Earth's viewpoint to shift southward. Though most of the constellation was visible in Classical times, the constellation is now not easily visible from most of the northern hemisphere. All the stars of Argo Navis are easily visible from the tropics southward and pass near zenith from southern temperate latitudes. The brightest of these is Canopus (α Carinae), the second-brightest night-time star, now assigned to Carina.
History
Development of the Greek constellation
Argo Navis is known from Greek texts, which derived it from Egypt around 1000 BC. Plutarch attributed it to the Egyptian "Boat of Osiris." Some academics theorized a Sumerian origin related to the Epic of Gilgamesh, a hypothesis rejected for lack of evidence that Mesopotamian cultures considered these stars, or any portion of them, to form a boat. | Argo Navis | Wikipedia | 439 | 1924 | https://en.wikipedia.org/wiki/Argo%20Navis | Physical sciences | Asterism | Astronomy |
Over time, Argo became identified exclusively with ancient Greek myth of Jason and the Argonauts. In Ptolemy's Almagest, Argo Navis occupies the portion of the Milky Way between Canis Major and Centaurus, with stars marking such details as the "little shield", the "steering-oar", the "mast-holder", and the "stern-ornament", which continued to be reflected in cartographic representations in celestial atlases into the nineteenth century (see below). The ship appeared to rotate about the pole sternwards, so nautically in reverse. Aratus, the Greek poet / historian living in the third century BCE, noted this backward progression writing, "Argo by the Great Dog's [Canis Major's] tail is drawn; for hers is not a usual course, but backward turned she comes ...".
The constituent modern constellations
In modern times, Argo Navis was considered unwieldy due to its enormous size (28% larger than Hydra, the largest modern constellation). In his 1763 star catalogue, Nicolas Louis de Lacaille explained that there were more than a hundred and sixty stars clearly visible to the naked eye in Navis, and so he used the set of lowercase and uppercase Latin letters three times on portions of the constellation referred to as "Argûs in carina" (Carina, the keel), "Argûs in puppi" (Puppis, the poop deck or stern), and "Argûs in velis" (Vela, the sails). Lacaille replaced Bayer's designations with new ones that followed stellar magnitudes more closely, but used only a single Greek-letter sequence and described the constellation for those stars as "Argûs". Similarly, faint unlettered stars were listed only as in "Argûs". | Argo Navis | Wikipedia | 381 | 1924 | https://en.wikipedia.org/wiki/Argo%20Navis | Physical sciences | Asterism | Astronomy |
The final breakup and abolition of Argo Navis was proposed by Sir John Herschel in 1841 and again in 1844. Despite this, the constellation remained in use in parallel with its constituent parts into the 20th century. In 1922, along with the other constellations, it received a three-letter abbreviation: Arg. The breakup and relegation to a former constellation occurred in 1930 when the IAU defined the 88 modern constellations, formally instituting Carina, Puppis, and Vela, and declaring Argo obsolete. Lacaille's designations were kept in the offspring, so Carina has α, β, and ε; Vela has γ and δ; Puppis has ζ; and so on. As a result of this breakup, Argo Navis is the only one of Ptolemy's 48 constellations that is no longer officially recognized as a single constellation.
In addition, the constellation Pyxis (the mariner's compass) occupies an area near what in antiquity was considered part of Argo's mast. Some recent authors state that the compass was part of the ship, but magnetic compasses were unknown in ancient Greek times. Lacaille considered it a separate constellation representing a modern scientific instrument (like Microscopium and Telescopium), that he created for maps of the stars of the southern hemisphere. Pyxis was listed among his 14 new constellations. In 1844, John Herschel suggested formalizing the mast as a new constellation, Malus, to replace Lacaille's Pyxis, but the idea did not catch on. Similarly, an effort by Edmond Halley to detach the "cloud of mist" at the prow of Argo Navis to form a new constellation named Robur Carolinum (Charles' Oak) in honor of King Charles II, his patron, was unsuccessful.
Representations in other cultures
In Vedic period astronomy, which drew its zodiac signs and many constellations from the period of the Indo-Greek Kingdom, Indian observers saw the asterism as a boat.
The Māori had several names for the constellation, including Te Waka-o-Tamarereti (the canoe of Tamarereti), Te Kohi-a-Autahi (an expression meaning "cold of autumn settling down on land and water"), and Te Kohi. | Argo Navis | Wikipedia | 479 | 1924 | https://en.wikipedia.org/wiki/Argo%20Navis | Physical sciences | Asterism | Astronomy |
Antlia (; from Ancient Greek ἀντλία) is a constellation in the Southern Celestial Hemisphere. Its name means "pump" in Latin and Greek; it represents an air pump. Originally Antlia Pneumatica, the constellation was established by Nicolas-Louis de Lacaille in the 18th century. Its non-specific (single-word) name, already in limited use, was preferred by John Herschel then welcomed by the astronomic community which officially accepted this. North of stars forming some of the sails of the ship Argo Navis (the constellation Vela), Antlia is completely visible from latitudes south of 49 degrees north.
Antlia is a faint constellation; its brightest star is Alpha Antliae, an orange giant that is a suspected variable star, ranging between apparent magnitudes 4.22 and 4.29. S Antliae is an eclipsing binary star system, changing in brightness as one star passes in front of the other. Sharing a common envelope, the stars are so close they will one day merge to form a single star. Two star systems with known exoplanets, HD 93083 and WASP-66, lie within Antlia, as do NGC 2997, a spiral galaxy, and the Antlia Dwarf Galaxy.
History
The French astronomer Nicolas-Louis de Lacaille first described the constellation in French as la Machine Pneumatique (the Pneumatic Machine) in 1751–52, commemorating the air pump invented by the French physicist Denis Papin. De Lacaille had observed and catalogued almost 10,000 southern stars during a two-year stay at the Cape of Good Hope, devising fourteen new constellations in uncharted regions of the Southern Celestial Hemisphere not visible from Europe. He named all but one in honour of instruments that symbolised the Age of Enlightenment. Lacaille depicted Antlia as a single-cylinder vacuum pump used in Papin's initial experiments, while German astronomer Johann Bode chose the more advanced double-cylinder version. Lacaille Latinised the name to Antlia pneumatica on his 1763 chart. English astronomer John Herschel proposed shrinking the name to one word in 1844, noting that Lacaille himself had abbreviated his constellations thus on occasion. This was universally adopted. The International Astronomical Union adopted it as one of the 88 modern constellations in 1922. | Antlia | Wikipedia | 485 | 1926 | https://en.wikipedia.org/wiki/Antlia | Physical sciences | Other | Astronomy |
Although visible to the Ancient Greeks, Antlia's stars were too faint to have been commonly recognised as a figurative object, or part of one, in ancient asterisms. The stars that now comprise Antlia are in a zone of the sky associated with the asterism/old constellation Argo Navis, the ship, the Argo, of the Argonauts, in its latter centuries. This, due to its immense size, was split into hull, poop deck and sails by Lacaille in 1763. Ridpath reports that due to their faintness, the stars of Antlia did not make up part of the classical depiction of Argo Navis.
In non-Western astronomy
Chinese astronomers were able to view what is modern Antlia from their latitudes, and incorporated its stars into two different constellations. Several stars in the southern part of Antlia were a portion of "Dong'ou", which represented an area in southern China. Furthermore, Epsilon, Eta, and Theta Antliae were incorporated into the celestial temple, which also contained stars from modern Pyxis.
Characteristics
Covering 238.9 square degrees and hence 0.579% of the sky, Antlia ranks 62nd of the 88 modern constellations by area. Its position in the Southern Celestial Hemisphere means that the whole constellation is visible to observers south of 49°N. Hydra the sea snake runs along the length of its northern border, while Pyxis the compass, Vela the sails, and Centaurus the centaur line it to the west, south and east respectively. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union, is "Ant". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon with an east side, south side and ten other sides (facing the two other cardinal compass points) (illustrated in infobox at top-right). In the equatorial coordinate system, the right ascension coordinates of these borders lie between and , while the declination coordinates are between −24.54° and −40.42°.
Features
Stars | Antlia | Wikipedia | 435 | 1926 | https://en.wikipedia.org/wiki/Antlia | Physical sciences | Other | Astronomy |
Lacaille gave nine stars Bayer designations, labelling them Alpha through to Theta, combining two stars next to each other as Zeta. Gould later added a tenth, Iota Antliae. Beta and Gamma Antliae (now HR 4339 and HD 90156) ended up in the neighbouring constellation Hydra once the constellation boundaries were delineated in 1930. Within the constellation's borders, there are 42 stars brighter than or equal to apparent magnitude 6.5.
The constellation's two brightest stars—Alpha and Epsilon Antliae—shine with a reddish tinge. Alpha is an orange giant of spectral type K4III that is a suspected variable star, ranging between apparent magnitudes 4.22 and 4.29. It is located 320 ± 10 light-years away from Earth. Estimated to be shining with around 480 to 555 times the luminosity of the Sun, it is most likely an ageing star that is brightening and on its way to becoming a Mira variable star, having converted all its core fuel into carbon. Located 590 ± 30 light-years from Earth, Epsilon Antliae is an evolved orange giant star of spectral type K3 IIIa, that has swollen to have a diameter about 69 times that of the Sun, and a luminosity of around 1279 Suns. It is slightly variable. At the other end of Antlia, Iota Antliae is likewise an orange giant of spectral type K1 III. It is 202 ± 2 light-years distant. | Antlia | Wikipedia | 306 | 1926 | https://en.wikipedia.org/wiki/Antlia | Physical sciences | Other | Astronomy |
Located near Alpha is Delta Antliae, a binary star, 450 ± 10 light-years distant from Earth. The primary is a blue-white main sequence star of spectral type B9.5V and magnitude 5.6, and the secondary is a yellow-white main sequence star of spectral type F9Ve and magnitude 9.6. Zeta Antliae is a wide optical double star. The brighter star—Zeta1 Antliae—is 410 ± 40 light-years distant and has a magnitude of 5.74, though it is a true binary star system composed of two white main sequence stars of magnitudes 6.20 and 7.01 that are separated by 8.042 arcseconds. The fainter star—Zeta2 Antliae—is 386 ± 5 light-years distant and of magnitude 5.9. Eta Antliae is another double composed of a yellow white star of spectral type F1V and magnitude 5.31, with a companion of magnitude 11.3. Theta Antliae is likewise double, most likely composed of an A-type main sequence star and a yellow giant. S Antliae is an eclipsing binary star system that varies in apparent magnitude from 6.27 to 6.83 over a period of 15.6 hours. The system is classed as a W Ursae Majoris variable—the primary is hotter than the secondary and the drop in magnitude is caused by the latter passing in front of the former. Calculating the properties of the component stars from the orbital period indicates that the primary star has a mass 1.94 times and a diameter 2.026 times that of the Sun, and the secondary has a mass 0.76 times and a diameter 1.322 times that of the Sun. The two stars have similar luminosity and spectral type as they have a common envelope and share stellar material. The system is thought to be around 5–6 billion years old. The two stars will eventually merge to form a single fast-spinning star. | Antlia | Wikipedia | 411 | 1926 | https://en.wikipedia.org/wiki/Antlia | Physical sciences | Other | Astronomy |
T Antliae is a yellow-white supergiant of spectral type F6Iab and Classical Cepheid variable ranging between magnitude 8.88 and 9.82 over 5.9 days. U Antliae is a red C-type carbon star and is an irregular variable that ranges between magnitudes 5.27 and 6.04. At 910 ± 50 light-years distant, it is around 5819 times as luminous as the Sun. BF Antliae is a Delta Scuti variable that varies by 0.01 of a magnitude. HR 4049, also known as AG Antliae, is an unusual hot variable ageing star of spectral type B9.5Ib-II. It is undergoing intense loss of mass and is a unique variable that does not belong to any class of known variable star, ranging between magnitudes 5.29 and 5.83 with a period of 429 days. It is around 6000 light-years away from Earth. UX Antliae is an R Coronae Borealis variable with a baseline apparent magnitude of around 11.85, with irregular dimmings down to below magnitude 18.0. A luminous and remote star, it is a supergiant with a spectrum resembling that of a yellow-white F-type star but it has almost no hydrogen.
HD 93083 is an orange dwarf star of spectral type K3V that is smaller and cooler than the Sun. It has a planet that was discovered by the radial velocity method with the HARPS spectrograph in 2005. About as massive as Saturn, the planet orbits its star with a period of 143 days at a mean distance of 0.477 AU. WASP-66 is a sunlike star of spectral type F4V. A planet with 2.3 times the mass of Jupiter orbits it every 4 days, discovered by the transit method in 2012. DEN 1048-3956 is a brown dwarf of spectral type M8 located around 13 light-years distant from Earth. At magnitude 17 it is much too faint to be seen with the unaided eye. It has a surface temperature of about 2500 K. Two powerful flares lasting 4–5 minutes each were detected in 2002. 2MASS 0939-2448 is a system of two cool and faint brown dwarfs, probably with effective temperatures of about 500 and 700 K and masses of about 25 and 40 times that of Jupiter, though it is also possible that both objects have temperatures of 600 K and 30 Jupiter masses.
Deep-sky objects | Antlia | Wikipedia | 512 | 1926 | https://en.wikipedia.org/wiki/Antlia | Physical sciences | Other | Astronomy |
Antlia contains many faint galaxies, the brightest of which is NGC 2997 at magnitude 10.6. It is a loosely wound face-on spiral galaxy of type Sc. Though nondescript in most amateur telescopes, it presents bright clusters of young stars and many dark dust lanes in photographs. Discovered in 1997, the Antlia Dwarf is a 14.8m dwarf spheroidal galaxy that belongs to the Local Group of galaxies. In 2018 the discovery was announced of a very low surface brightness galaxy near Epsilon Antliae, Antlia 2, which is a satellite galaxy of the Milky Way.
The Antlia Cluster, also known as Abell S0636, is a cluster of galaxies located in the Hydra–Centaurus Supercluster. It is the third nearest to the Local Group after the Virgo Cluster and the Fornax Cluster. The cluster's distance from earth is Located in the southeastern corner of the constellation, it boasts the giant elliptical galaxies NGC 3268 and NGC 3258 as the main members of a southern and northern subgroup respectively, and contains around 234 galaxies in total.
Antlia is home to the huge Antlia Supernova Remnant, one of the largest supernova remnants in the sky. | Antlia | Wikipedia | 248 | 1926 | https://en.wikipedia.org/wiki/Antlia | Physical sciences | Other | Astronomy |
Ara (Latin for "the Altar") is a southern constellation between Scorpius, Telescopium, Triangulum Australe, and Norma. It was (as ) one of the Greek bulk (namely 48) described by the 2nd-century astronomer Ptolemy, and it remains one of the 88 modern constellations designated by the International Astronomical Union.
The orange supergiant Beta Arae, to us its brightest star measured with near-constant apparent magnitude of 2.85, is marginally brighter than blue-white Alpha Arae. Seven star systems are known to host planets. Sunlike Mu Arae hosts four known planets. Gliese 676 is a (gravity-paired) binary red dwarf system with four known planets.
The Milky Way crosses the northwestern part of Ara. Within the constellation is Westerlund 1, a super star cluster that contains the red supergiant Westerlund 1-26, one of the largest stars known.
History
In ancient Greek mythology, Ara was identified as the altar where the gods first made offerings and formed an alliance before defeating the Titans. One of the southernmost constellations depicted by Ptolemy, it had been recorded by Aratus in 270 BC as lying close to the horizon, and the Almagest portrays stars as far south as Gamma Arae. Professor Bradley Schaefer proposes such Ancients must have been able to see as far south as Zeta Arae, for a pattern that looked like an altar.
In illustrations, Ara is usually depicted as compact classical altar with its smoke 'rising' southward. However, depictions often vary. In the early days of printing, a 1482 woodcut of Gaius Julius Hyginus's classic Poeticon Astronomicon depicts the altar as surrounded by demons. Johann Bayer in 1603 depicted Ara as an altar with burning incense. Indeed, frankincense burners were common throughout the Levant especially in the Yemen, where they are known as Mabkhara. This required live coals or burning embers called Jamra', in order to burn the incense. Willem Blaeu, a Dutch uranographer of the 16th and 17th centuries, drew Ara as an altar for sacrifices, with a burning animal offering unusually whose smoke rises northward, represented by Alpha Arae. | Ara (constellation) | Wikipedia | 462 | 1927 | https://en.wikipedia.org/wiki/Ara%20%28constellation%29 | Physical sciences | Other | Astronomy |
The Castle of Knowledge by Robert Record of 1556 lists the constellation stating that "Under the Scorpions tayle, standeth the Altar."; a decade later a translation of a fairly recent mainly astrological work by Marcellus Palingenius of 1565, by Barnabe Googe states "Here mayst thou both the Altar, and the myghty Cup beholde."
Equivalents
In Chinese astronomy, the stars of the constellation Ara lie within The Azure Dragon of the East (, ). Five stars of Ara formed (), a tortoise, while another three formed (), a pestle.
The Wardaman people of the Northern Territory in Australia saw the stars of Ara and the neighbouring constellation Pavo as flying foxes.
Characteristics
Covering 237.1 square degrees and hence 0.575% of the sky, Ara ranks 63rd of the 88 modern constellations by area. Its position in the Southern Celestial Hemisphere means that the whole constellation is visible to observers south of 22°N. Scorpius runs along the length of its northern border, while Norma and Triangulum Australe border it to the west, Apus to the south, and Pavo and Telescopium to the east respectively. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union, is "Ara". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of twelve segments. In the equatorial coordinate system, the right ascension coordinates of these borders lie between and , while the declination coordinates are between −45.49° and −67.69°.
Features
Stars
Bayer gave eight stars Bayer designations, labelling them Alpha through to Theta, though he had never seen the constellation directly as it never rises above the horizon in Germany. After charting the southern constellations, French astronomer Nicolas-Louis de Lacaille recharted the stars of Ara from Alpha through to Sigma, including three pairs of stars next to each other as Epsilon, Kappa and Nu.
Ara contains part of the Milky Way to the south of Scorpius and thus has rich star fields. Within the constellation's borders, there are 71 stars brighter than or equal to apparent magnitude 6.5. | Ara (constellation) | Wikipedia | 463 | 1927 | https://en.wikipedia.org/wiki/Ara%20%28constellation%29 | Physical sciences | Other | Astronomy |
Beta Arae, apparent magnitude 2.85, is the brightest star in the constellation, about 0.1 mag brighter than Alpha Arae although the difference in brightness between the two is undetectable by the unaided eye. Beta is an orange-hued star of spectral type K3Ib-IIa that has been classified as a supergiant or bright giant, and lies around 650 light-years from Earth. It is over 8 times as massive and 5,636 times as luminous as the Sun. Close to Beta Arae is Gamma Arae, a blue-hued supergiant of spectral type B1Ib. Of apparent magnitude 3.3, it is 1110 ± 60 light-years from Earth. It has been estimated to be between 12.5 and 25 times as massive as the Sun, and have around 120,000 times its luminosity.
Alpha Arae is a blue-white main sequence star of magnitude 2.95, that is 270 ± 20 light-years from Earth. This star is around 9.6 times as massive as the Sun, and has an average of 4.5 times its radius. It is 5,800 times as luminous as the Sun, its energy emitted from its outer envelope at an effective temperature of 18,044 K. A Be star, Alpha Arae is surrounded by a dense equatorial disk of material in Keplerian (rather than uniform) rotation. The star is losing mass by a polar stellar wind with a terminal velocity of approximately 1,000 km/s.
The third brightest star in Ara at magnitude 3.13 is Zeta Arae, an orange giant of spectral type K3III that is located 490 ± 10 light-years from Earth. Around 7–8 times as massive as the Sun, it has swollen to a diameter around 114 times that of the Sun and is 3800 times as luminous. Were it not dimmer by intervening interstellar dust, it would be significantly brighter at magnitude 2.11.
Delta Arae is a blue-white main sequence star of spectral type B8Vn and magnitude 3.6, 198 ± 4 light-years from Earth. It is around 3.56 times as massive as the Sun. | Ara (constellation) | Wikipedia | 448 | 1927 | https://en.wikipedia.org/wiki/Ara%20%28constellation%29 | Physical sciences | Other | Astronomy |
Epsilon1 Arae is an orange giant of apparent magnitude 4.1, 360 ± 10 light-years distant from Earth. It is around 74% more massive than the Sun. At an age of about 1.7 billion years, the outer envelope of the star has expanded to almost 34 times the Sun's radius.
Eta Arae is an orange giant of apparent magnitude 3.76, located 299 ± 5 light-years distant from Earth. Estimated to be around five billion years old, it has reached the giant star stage of its evolution. With 1.12 times the mass of the Sun, it has an outer envelope that has expanded to 40 times the Sun's radius. The star is now spinning so slowly that it takes more than eleven years to complete a single rotation.
GX 339-4 (V821 Arae) is a moderately strong variable galactic low-mass X-ray binary (LMXB) source and black-hole candidate that flares from time to time. From spectroscopic measurements, the mass of the black-hole was found to be at least of 5.8 solar masses.
Exoplanets have been discovered in seven star systems in the constellation. Mu Arae (Cervantes) is a sunlike star that hosts four planets. HD 152079 is a sunlike star with a jupiter-like planet with an orbital period of 2097 ± 930 days. HD 154672 is an ageing sunlike star with a Hot Jupiter. HD 154857 is a sunlike star with one confirmed and one suspected planet. HD 156411 is a star hotter and larger than the sun with a gas giant planet in orbit. Gliese 674 is a nearby red dwarf star with a planet. Gliese 676 is a binary star system composed of two red dwarves with four planets.
Deep-sky objects
The northwest corner of Ara is crossed by the galactic plane of the Milky Way and contains several open clusters (notably NGC 6200) and diffuse nebulae (including the bright cluster/nebula pair NGC 6188 and NGC 6193). The brightest of the globular clusters, sixth magnitude NGC 6397, lies at a distance of just , making it one of the closest globular clusters to the Solar System. | Ara (constellation) | Wikipedia | 467 | 1927 | https://en.wikipedia.org/wiki/Ara%20%28constellation%29 | Physical sciences | Other | Astronomy |
Ara also contains Westerlund 1, a super star cluster containing itself the possible red supergiant Westerlund 1-237 and the red supergiant Westerlund 1-26. The latter is one of the largest stars known with an estimate varying between and .
Although Ara lies close to the heart of the Milky Way, two spiral galaxies (NGC 6215 and NGC 6221) are visible near star Eta Arae.
Open clusters
NGC 6193 is an open cluster containing approximately 30 stars with an overall magnitude of 5.0 and a size of 0.25 square degrees, about half the size of the full Moon. It is approximately 4200 light-years from Earth. It has one bright member, a double star with a blue-white hued primary of magnitude 5.6 and a secondary of magnitude 6.9. NGC 6193 is surrounded by NGC 6188, a faint nebula only normally visible in long-exposure photographs.
NGC 6200
NGC 6204
NGC 6208
NGC 6250
NGC 6253
IC 4651
Globular clusters
NGC 6352
NGC 6362
NGC 6397 is a globular cluster with an overall magnitude of 6.0; it is visible to the naked eye under exceptionally dark skies and is normally visible in binoculars. It is a fairly close globular cluster, at a distance of 10,500 light-years.
Planetary Nebulae
The Stingray Nebula (Hen 3–1357), the youngest known planetary nebula as of 2010, formed in Ara; the light from its formation was first observable around 1987.
NGC 6326. A planetary nebula that might have a binary system at its center. | Ara (constellation) | Wikipedia | 339 | 1927 | https://en.wikipedia.org/wiki/Ara%20%28constellation%29 | Physical sciences | Other | Astronomy |
Apus is a small constellation in the southern sky. It represents a bird-of-paradise, and its name means "without feet" in Greek because the bird-of-paradise was once wrongly believed to lack feet. First depicted on a celestial globe by Petrus Plancius in 1598, it was charted on a star atlas by Johann Bayer in his 1603 Uranometria. The French explorer and astronomer Nicolas Louis de Lacaille charted and gave the brighter stars their Bayer designations in 1756.
The five brightest stars are all reddish in hue. Shading the others at apparent magnitude 3.8 is Alpha Apodis, an orange giant that has around 48 times the diameter and 928 times the luminosity of the Sun. Marginally fainter is Gamma Apodis, another aging giant star. Delta Apodis is a double star, the two components of which are 103 arcseconds apart and visible with the naked eye. Two star systems have been found to have planets.
History
Apus was one of twelve constellations published by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman who had sailed on the first Dutch trading expedition, known as the Eerste Schipvaart, to the East Indies. It first appeared on a 35-cm (14 in) diameter celestial globe published in 1598 in Amsterdam by Plancius with Jodocus Hondius. De Houtman included it in his southern star catalogue in 1603 under the Dutch name De Paradijs Voghel, "The Bird of Paradise", and Plancius called the constellation Paradysvogel Apis Indica; the first word is Dutch for "bird of paradise". Apis (Latin for "bee") is assumed to have been a typographical error for avis ("bird"). | Apus | Wikipedia | 380 | 1933 | https://en.wikipedia.org/wiki/Apus | Physical sciences | Other | Astronomy |
After its introduction on Plancius's globe, the constellation's first known appearance in a celestial atlas was in German cartographer Johann Bayer's Uranometria of 1603. Bayer called it Apis Indica while fellow astronomers Johannes Kepler and his son-in-law Jakob Bartsch called it Apus or Avis Indica. The name Apus is derived from the Greek apous, meaning "without feet". This referred to the Western misconception that the bird-of-paradise had no feet, which arose because the only specimens available in the West had their feet and wings removed. Such specimens began to arrive in Europe in 1522, when the survivors of Ferdinand Magellan's expedition brought them home. The constellation later lost some of its tail when Nicolas-Louis de Lacaille used those stars to establish Octans in the 1750s.
Characteristics
Covering 206.3 square degrees and hence 0.5002% of the sky, Apus ranks 67th of the 88 modern constellations by area. Its position in the Southern Celestial Hemisphere means that the whole constellation is visible to observers south of 7°N. It is bordered by Ara, Triangulum Australe and Circinus to the north, Musca and Chamaeleon to the west, Octans to the south, and Pavo to the east. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Aps". The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930, are defined by a polygon of six segments (illustrated in infobox). In the equatorial coordinate system, the right ascension coordinates of these borders lie between and , while the declination coordinates are between −67.48° and −83.12°.
Features
Stars
Lacaille gave twelve stars Bayer designations, labelling them Alpha through to Kappa, including two stars next to each other as Delta and another two stars near each other as Kappa. Within the constellation's borders, there are 39 stars brighter than or equal to apparent magnitude 6.5. Beta, Gamma and Delta Apodis form a narrow triangle, with Alpha Apodis lying to the east. The five brightest stars are all red-tinged, which is unusual among constellations. | Apus | Wikipedia | 471 | 1933 | https://en.wikipedia.org/wiki/Apus | Physical sciences | Other | Astronomy |
Alpha Apodis is an orange giant of spectral type K3III located 430 ± 20 light-years away from Earth, with an apparent magnitude of 3.8. It spent much of its life as a blue-white (B-type) main sequence star before expanding, cooling and brightening as it used up its core hydrogen. It has swollen to 48 times the Sun's diameter, and shines with a luminosity approximately 928 times that of the Sun, with a surface temperature of 4312 K. Beta Apodis is an orange giant 149 ± 2 light-years away, with a magnitude of 4.2. It is around 1.84 times as massive as the Sun, with a surface temperature of 4677 K. Gamma Apodis is a yellow giant of spectral type G8III located 150 ± 4 light-years away, with a magnitude of 3.87. It is approximately 63 times as luminous the Sun, with a surface temperature of 5279 K. Delta Apodis is a double star, the two components of which are 103 arcseconds apart and visible through binoculars. Delta1 is a red giant star of spectral type M4III located 630 ± 30 light-years away. It is a semiregular variable that varies from magnitude +4.66 to +4.87, with pulsations of multiple periods of 68.0, 94.9 and 101.7 days. Delta2 is an orange giant star of spectral type K3III, located 550 ± 10 light-years away, with a magnitude of 5.3. The separate components can be resolved with the naked eye.
The fifth-brightest star is Zeta Apodis at magnitude 4.8, a star that has swollen and cooled to become an orange giant of spectral type K1III, with a surface temperature of 4649 K and a luminosity 133 times that of the Sun. It is 300 ± 4 light-years distant. Near Zeta is Iota Apodis, a binary star system 1,040 ± 60 light-years distant, that is composed of two blue-white main sequence stars that orbit each other every 59.32 years. Of spectral types B9V and B9.5 V, they are both over three times as massive as the Sun. | Apus | Wikipedia | 472 | 1933 | https://en.wikipedia.org/wiki/Apus | Physical sciences | Other | Astronomy |
Eta Apodis is a white main sequence star located 140.8 ± 0.9 light-years distant. Of apparent magnitude 4.89, it is 1.77 times as massive, 15.5 times as luminous as the Sun and has 2.13 times its radius. Aged 250 ± 200 million years old, this star is emitting an excess of 24 μm infrared radiation, which may be caused by a debris disk of dust orbiting at a distance of more than 31 astronomical units from it.
Theta Apodis is a cool red giant of spectral type M7 III located 350 ± 30 light-years distant. It shines with a luminosity approximately 3879 times that of the Sun and has a surface temperature of 3151 K. A semiregular variable, it varies by 0.56 magnitudes with a period of 119 days—or approximately 4 months. It is losing mass at the rate of times the mass of the Sun per year through its stellar wind. Dusty material ejected from this star is interacting with the surrounding interstellar medium, forming a bow shock as the star moves through the galaxy. NO Apodis is a red giant of spectral type M3III that varies between magnitudes 5.71 and 5.95. Located 780 ± 20 light-years distant, it shines with a luminosity estimated at 2059 times that of the Sun and has a surface temperature of 3568 K. S Apodis is a rare R Coronae Borealis variable, an extremely hydrogen-deficient supergiant thought to have arisen as the result of the merger of two white dwarfs; fewer than 100 have been discovered as of 2012. It has a baseline magnitude of 9.7. R Apodis is a star that was given a variable star designation, yet has turned out not to be variable. Of magnitude 5.3, it is another orange giant. | Apus | Wikipedia | 385 | 1933 | https://en.wikipedia.org/wiki/Apus | Physical sciences | Other | Astronomy |
Two star systems have had exoplanets discovered by doppler spectroscopy, and the substellar companion of a third star system—the sunlike star HD 131664—has since been found to be a brown dwarf with a calculated mass of the companion to 23 times that of Jupiter (minimum of 18 and maximum of 49 Jovian masses). HD 134606 is a yellow sunlike star of spectral type G6IV that has begun expanding and cooling off the main sequence. Three planets orbit it with periods of 12, 59.5 and 459 days, successively larger as they are further away from the star. HD 137388 is another star—of spectral type K2IV—that is cooler than the Sun and has begun cooling off the main sequence. Around 47% as luminous and 88% as massive as the Sun, with 85% of its diameter, it is thought to be around 7.4 ± 3.9 billion years old. It has a planet that is 79 times as massive as the Earth and orbits its sun every 330 days at an average distance of 0.89 astronomical units (AU).
Deep-sky objects
The Milky Way covers much of the constellation's area. Of the deep-sky objects in Apus, there are two prominent globular clusters—NGC 6101 and IC 4499—and a large faint nebula that covers several degrees east of Beta and Gamma Apodis. NGC 6101 is a globular cluster of apparent magnitude 9.2 located around 50,000 light-years distant from Earth, which is around 160 light-years across. Around 13 billion years old, it contains a high concentration of massive bright stars known as blue stragglers, thought to be the result of two stars merging. IC 4499 is a loose globular cluster in the medium-far galactic halo; its apparent magnitude is 10.6.
The galaxies in the constellation are faint. IC 4633 is a very faint spiral galaxy surrounded by a vast amount of Milky Way line-of-sight integrated flux nebulae—large faint clouds thought to be lit by large numbers of stars. | Apus | Wikipedia | 433 | 1933 | https://en.wikipedia.org/wiki/Apus | Physical sciences | Other | Astronomy |
The word aeon , also spelled eon (in American and Australian English), originally meant "life", "vital force" or "being", "generation" or "a period of time", though it tended to be translated as "age" in the sense of "ages", "forever", "timeless" or "for eternity". It is a Latin transliteration from the ancient Greek word (), from the archaic () meaning "century". In Greek, it literally refers to the timespan of one hundred years. A cognate Latin word (cf. ) for "age" is present in words such as eternal, longevity and mediaeval.
Although the term aeon may be used in reference to a period of a billion years (especially in geology, cosmology and astronomy), its more common usage is for any long, indefinite period. Aeon can also refer to the four aeons on the geologic time scale that make up the Earth's history, the Hadean, Archean, Proterozoic, and the current aeon, Phanerozoic.
Astronomy and cosmology
In astronomy, an aeon is defined as a billion years (109 years, abbreviated AE).
Roger Penrose uses the word aeon to describe the period between successive and cyclic Big Bangs within the context of conformal cyclic cosmology.
Philosophy and mysticism
In Buddhism, an "aeon" or (Sanskrit: ) is often said to be 1,334,240,000 years, the life cycle of the world. Yet, these numbers are symbolic, not literal.
Christianity's idea of "eternal life" comes from the word for life, (), and a form of (), which could mean life in the next aeon, the Kingdom of God, or Heaven, just as much as immortality, as in John 3:16. | Aeon | Wikipedia | 389 | 1941 | https://en.wikipedia.org/wiki/Aeon | Physical sciences | Time | Basics and measurement |
According to Christian universalism, the Greek New Testament scriptures use the word () to mean a long period and the word () to mean "during a long period"; thus, there was a time before the aeons, and the aeonian period is finite. After each person's mortal life ends, they are judged worthy of aeonian life or aeonian punishment. That is, after the period of the aeons, all punishment will cease and death is overcome and then God becomes the all in each one (1Cor 15:28). This contrasts with the conventional Christian belief in eternal life and eternal punishment.
Occultists of the Thelema and Ordo Templi Orientis (English: "Order of the Temple of the East") traditions sometimes speak of a "magical Aeon" that may last for perhaps as little as 2,000 years.
Gnosticism
In many Gnostic systems, the various emanations of God, who is also known by such names as the One, the Monad, Aion teleos ("The Broadest Aeon", Greek: ), Bythos ("depth or profundity", Greek: ), Proarkhe ("before the beginning", Greek: ), ("the beginning", Greek: ), ("wisdom"), and ("the Anointed One"), are called Aeons. In the different systems these emanations are differently named, classified, and described, but the emanation theory itself is common to all forms of Gnosticism.
In the Basilidian Gnosis they are called sonships ( ; singular: ); according to Marcus, they are numbers and sounds; in Valentinianism they form male/female pairs called "" (Greek , from ). | Aeon | Wikipedia | 373 | 1941 | https://en.wikipedia.org/wiki/Aeon | Physical sciences | Time | Basics and measurement |
An airline is a company that provides air transport services for traveling passengers or freight (cargo). Airlines use aircraft to supply these services and may form partnerships or alliances with other airlines for codeshare agreements, in which they both offer and operate the same flight. Generally, airline companies are recognized with an air operating certificate or license issued by a governmental aviation body. Airlines may be scheduled or charter operators.
The first airline was the German airship company DELAG, founded on November 16, 1909. The four oldest non-airship airlines that still exist are the Netherlands' KLM (1919), Colombia's Avianca (1919), Australia's Qantas (1920) and the Russian Aeroflot (1923).
Airline ownership has seen a shift from mostly personal ownership until the 1930s to government-ownership of major airlines from the 1940s to 1980s and back to large-scale privatization following the mid-1980s. Since the 1980s, there has been a trend of major airline mergers and the formation of airline alliances. The largest alliances are Star Alliance, SkyTeam and Oneworld. Airline alliances coordinate their passenger service programs (such as lounges and frequent-flyer programs), offer special interline tickets and often engage in extensive codesharing (sometimes systemwide).
History
The first airlines
DELAG, Deutsche Luftschiffahrts-Aktiengesellschaft I was the world's first airline. It was founded on November 16, 1909, with government assistance, and operated airships manufactured by The Zeppelin Corporation. Its headquarters were in Frankfurt.
The first fixed-wing scheduled airline was started on January 1, 1914. The flight was piloted by Tony Jannus and flew from St. Petersburg, Florida, to Tampa, Florida, operated by the St. Petersburg–Tampa Airboat Line.
Europe
Beginnings | Airline | Wikipedia | 366 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
The earliest fixed wing airline in Europe was Aircraft Transport and Travel, formed by George Holt Thomas in 1916; via a series of takeovers and mergers, this company is an ancestor of modern-day British Airways. Using a fleet of former military Airco DH.4A biplanes that had been modified to carry two passengers in the fuselage, it operated relief flights between Folkestone and Ghent, Belgium. On July 15, 1919, the company flew a proving flight across the English Channel, despite a lack of support from the British government. Flown by Lt. H Shaw in an Airco DH.9 between RAF Hendon and Paris – Le Bourget Airport, the flight took 2 hours and 30 minutes at £21 per passenger.
On August 25, 1919, the company used DH.16s to pioneer a regular service from Hounslow Heath Aerodrome to Paris's Le Bourget, the first regular international service in the world. The airline soon gained a reputation for reliability, despite problems with bad weather, and began to attract European competition. In November 1919, it won the first British civil airmail contract. Six Royal Air Force Airco DH.9A aircraft were lent to the company, to operate the airmail service between Hawkinge and Cologne. In 1920, they were returned to the Royal Air Force.
Other British competitors were quick to follow – Handley Page Transport was established in 1919 and used the company's converted wartime Type O/400 bombers with a capacity for 12 passengers, to run a London-Paris passenger service.
The first French airline was Société des lignes Latécoère, later known as Aéropostale, which started its first service in late 1918 to Spain. The Société Générale des Transports Aériens was created in late 1919, by the Farman brothers and the Farman F.60 Goliath plane flew scheduled services from Toussus-le-Noble to Kenley, near Croydon, England. Another early French airline was the Compagnie des Messageries Aériennes, established in 1919 by Louis-Charles Breguet, offering a mail and freight service between Le Bourget Airport, Paris and Lesquin Airport, Lille. | Airline | Wikipedia | 443 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
The first German airline to use heavier than air aircraft was Deutsche Luft-Reederei established in 1917 which started operating in February 1919. In its first year, the D.L.R. operated regularly scheduled flights on routes with a combined length of nearly 1000 miles. By 1921 the D.L.R. network was more than 3000 km (1865 miles) long, and included destinations in the Netherlands, Scandinavia and the Baltic Republics. Another important German airline was Junkers Luftverkehr, which began operations in 1921. It was a division of the aircraft manufacturer Junkers, which became a separate company in 1924. It operated joint-venture airlines in Austria, Denmark, Estonia, Finland, Hungary, Latvia, Norway, Poland, Sweden and Switzerland.
The Dutch airline KLM made its first flight in 1920, and is the oldest continuously operating airline in the world. Established by aviator Albert Plesman, it was immediately awarded a "Royal" predicate from Queen Wilhelmina. Its first flight was from Croydon Airport, London to Amsterdam, using a leased Aircraft Transport and Travel DH-16, and carrying two British journalists and a number of newspapers. In 1921, KLM started scheduled services.
In Finland, the charter establishing Aero O/Y (now Finnair) was signed in the city of Helsinki on 12 September 1923. Junkers F.13 D-335 became the first aircraft of the company, when Aero took delivery of it on 14 March 1924. The first flight was between Helsinki and Tallinn, capital of Estonia, and it took place on 20 March 1924, one week later.
In the Soviet Union, the Chief Administration of the Civil Air Fleet was established in 1921. One of its first acts was to help found Deutsch-Russische Luftverkehrs A.G. (Deruluft), a German-Russian joint venture to provide air transport from Russia to the West. Domestic air service began around the same time, when Dobrolyot started operations on 15 July 1923 between Moscow and Nizhni Novgorod. Since 1932 all operations had been carried under the name Aeroflot.
Early European airlines tended to favor comfort – the passenger cabins were often spacious with luxurious interiors – over speed and efficiency. The relatively basic navigational capabilities of pilots at the time also meant that delays due to the weather were commonplace.
Rationalization | Airline | Wikipedia | 477 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
By the early 1920s, small airlines were struggling to compete, and there was a movement towards increased rationalization and consolidation. In 1924, Imperial Airways was formed from the merger of Instone Air Line Company, British Marine Air Navigation, Daimler Airway and Handley Page Transport, to allow British airlines to compete with stiff competition from French and German airlines that were enjoying heavy government subsidies. The airline was a pioneer in surveying and opening up air routes across the world to serve far-flung parts of the British Empire and to enhance trade and integration.
The first new airliner ordered by Imperial Airways, was the Handley Page W8f City of Washington, delivered on 3 November 1924. In the first year of operation the company carried 11,395 passengers and 212,380 letters. In April 1925, the film The Lost World became the first film to be screened for passengers on a scheduled airliner flight when it was shown on the London-Paris route.
Two French airlines also merged to form Air Union on 1 January 1923. This later merged with four other French airlines to become Air France, the country's flagship carrier to this day, on 17 May 1933.
Germany's Deutsche Lufthansa was created in 1926 by merger of two airlines, one of them Junkers Luftverkehr. Lufthansa, due to the Junkers heritage and unlike most other airlines at the time, became a major investor in airlines outside of Europe, providing capital to Varig and Avianca. German airliners built by Junkers, Dornier, and Fokker were among the most advanced in the world at the time.
Expansion
In 1926, Alan Cobham surveyed a flight route from the UK to Cape Town, South Africa, following this up with another proving flight to Melbourne, Australia. Other routes to British India and the Far East were also charted and demonstrated at this time. Regular services to Cairo and Basra began in 1927 and were extended to Karachi in 1929. The London-Australia service was inaugurated in 1932 with the Handley Page HP 42 airliners. Further services were opened up to Calcutta, Rangoon, Singapore, Brisbane and Hong Kong passengers departed London on 14 March 1936 following the establishment of a branch from Penang to Hong Kong.
France began an air mail service to Morocco in 1919 that was bought out in 1927, renamed Aéropostale, and injected with capital to become a major international carrier. In 1933, Aéropostale went bankrupt, was nationalized and merged into Air France. | Airline | Wikipedia | 504 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
Although Germany lacked colonies, it also began expanding its services globally. In 1931, the airship Graf Zeppelin began offering regular scheduled passenger service between Germany and South America, usually every two weeks, which continued until 1937. In 1936, the airship Hindenburg entered passenger service and successfully crossed the Atlantic 36 times before crashing at Lakehurst, New Jersey, on 6 May 1937. In 1938, a weekly air service from Berlin to Kabul, Afghanistan, started operating.
From February 1934 until World War II began in 1939, Deutsche Lufthansa operated an airmail service from Stuttgart, Germany via Spain, the Canary Islands and West Africa to Natal in Brazil. This was the first time an airline flew across an ocean.
By the end of the 1930s Aeroflot had become the world's largest airline, employing more than 4,000 pilots and 60,000 other service personnel and operating around 3,000 aircraft (of which 75% were considered obsolete by its own standards). During the Soviet era Aeroflot was synonymous with Russian civil aviation, as it was the only air carrier. It became the first airline in the world to operate sustained regular jet services on 15 September 1956 with the Tupolev Tu-104.
Deregulation
Deregulation of the European Union airspace in the early 1990s has had substantial effect on the structure of the industry there. The shift towards 'budget' airlines on shorter routes has been significant. Airlines such as EasyJet and Ryanair have often grown at the expense of the traditional national airlines.
There has also been a trend for these national airlines themselves to be privatized such as has occurred for Aer Lingus and British Airways. Other national airlines, including Italy's Alitalia, suffered – particularly with the rapid increase of oil prices in early 2008.
United States
Early development | Airline | Wikipedia | 363 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
Tony Jannus conducted the United States' first scheduled commercial airline flight on January 1, 1914, for the St. Petersburg-Tampa Airboat Line. The 23-minute flight traveled between St. Petersburg, Florida and Tampa, Florida, passing some above Tampa Bay in Jannus' Benoist XIV wood and muslin biplane flying boat. His passenger was a former mayor of St. Petersburg, who paid $400 for the privilege of sitting on a wooden bench in the open cockpit. The Airboat line operated for about four months, carrying more than 1,200 passengers who paid $5 each. Chalk's International Airlines began service between Miami and Bimini in the Bahamas in February 1919. Based in Ft. Lauderdale, Chalk's claimed to be the oldest continuously operating airline in the United States until its closure in 2008.
Following World War I, the United States found itself swamped with aviators. Many decided to take their war-surplus aircraft on barnstorming campaigns, performing aerobatic maneuvers to woo crowds. In 1918, the United States Postal Service won the financial backing of Congress to begin experimenting with air mail service, initially using Curtiss Jenny aircraft that had been procured by the United States Army Air Service. Private operators were the first to fly the mail but due to numerous accidents the US Army was tasked with mail delivery. During the Army's involvement they proved to be too unreliable and lost their air mail duties. By the mid-1920s, the Postal Service had developed its own air mail network, based on a transcontinental backbone between New York City and San Francisco. To supplement this service, they offered twelve contracts for spur routes to independent bidders. Some of the carriers that won these routes would, through time and mergers, evolve into Pan Am, Delta Air Lines, Braniff Airways, American Airlines, United Airlines (originally a division of Boeing), Trans World Airlines, Northwest Airlines, and Eastern Air Lines.
Service during the early 1920s was sporadic: most airlines at the time were focused on carrying bags of mail. In 1925, however, the Ford Motor Company bought out the Stout Aircraft Company and began construction of the all-metal Ford Trimotor, which became the first successful American airliner. With a 12-passenger capacity, the Trimotor made passenger service potentially profitable. Air service was seen as a supplement to rail service in the American transportation network. | Airline | Wikipedia | 482 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
At the same time, Juan Trippe began a crusade to create an air network that would link America to the world, and he achieved this goal through his airline, Pan Am, with a fleet of flying boats that linked Los Angeles to Shanghai and Boston to London. Pan Am and Northwest Airways (which began flights to Canada in the 1920s) were the only U.S. airlines to go international before the 1940s.
With the introduction of the Boeing 247 and Douglas DC-3 in the 1930s, the U.S. airline industry was generally profitable, even during the Great Depression. This trend continued until the beginning of World War II.
Since 1945
World War II, like World War I, brought new life to the airline industry. Many airlines in the Allied countries were flush from lease contracts to the military, and foresaw a future explosive demand for civil air transport, for both passengers and cargo. They were eager to invest in the newly emerging flagships of air travel such as the Boeing Stratocruiser, Lockheed Constellation, and Douglas DC-6. Most of these new aircraft were based on American bombers such as the B-29, which had spearheaded research into new technologies such as pressurization. Most offered increased efficiency from both added speed and greater payload.
In the 1950s, the De Havilland Comet, Boeing 707, Douglas DC-8, and Sud Aviation Caravelle became the first flagships of the Jet Age in the West, while the Eastern bloc had Tupolev Tu-104 and Tupolev Tu-124 in the fleets of state-owned carriers such as Czechoslovak ČSA, Soviet Aeroflot and East-German Interflug. The Vickers Viscount and Lockheed L-188 Electra inaugurated turboprop transport.
On 4 October 1958, British Overseas Airways Corporation started transatlantic flights between London Heathrow and New York Idlewild with a Comet 4, and Pan Am followed on 26 October with a Boeing 707 service between New York and Paris. | Airline | Wikipedia | 397 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
The next big boost for the airlines would come in the 1970s, when the Boeing 747, McDonnell Douglas DC-10, and Lockheed L-1011 inaugurated widebody ("jumbo jet") service, which is still the standard in international travel. The Tupolev Tu-144 and its Western counterpart, Concorde, made supersonic travel a reality. Concorde first flew in 1969 and operated through 2003. In 1972, Airbus began producing Europe's most commercially successful line of airliners to date. The added efficiencies for these aircraft were often not in speed, but in passenger capacity, payload, and range. Airbus also features modern electronic cockpits that were common across their aircraft to enable pilots to fly multiple models with minimal cross-training.
Deregulation
The 1978 U.S. airline industry deregulation lowered federally controlled barriers for new airlines just as a downturn in the nation's economy occurred. New start-ups entered during the downturn, during which time they found aircraft and funding, contracted hangar and maintenance services, trained new employees, and recruited laid-off staff from other airlines.
Major airlines dominated their routes through aggressive pricing and additional capacity offerings, often swamping new start-ups. In the place of high barriers to entry imposed by regulation, the major airlines implemented an equally high barrier called loss leader pricing. In this strategy an already established and dominant airline stomps out its competition by lowering airfares on specific routes, below the cost of operating on it, choking out any chance a start-up airline may have. The industry side effect is an overall drop in revenue and service quality. Since deregulation in 1978 the average domestic ticket price has dropped by 40%. So has airline employee pay. By incurring massive losses, the airlines of the USA now rely upon a scourge of cyclical Chapter 11 bankruptcy proceedings to continue doing business. America West Airlines (which has since merged with US Airways) remained a significant survivor from this new entrant era, as dozens, even hundreds, have gone under. | Airline | Wikipedia | 419 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
In many ways, the biggest winner in the deregulated environment was the air passenger. Although not exclusively attributable to deregulation, indeed the U.S. witnessed an explosive growth in demand for air travel. Many millions who had never or rarely flown before became regular fliers, even joining frequent flyer loyalty programs and receiving free flights and other benefits from their flying. New services and higher frequencies meant that business fliers could fly to another city, do business, and return the same day, from almost any point in the country. Air travel's advantages put long-distance intercity railroad travel and bus lines under pressure, with most of the latter having withered away, whilst the former is still protected under nationalization through the continuing existence of Amtrak.
By the 1980s, almost half of the total flying in the world took place in the U.S., and today the domestic industry operates over 10,000 daily departures nationwide.
Toward the end of the century, a new style of low cost airline emerged, offering a no-frills product at a lower price. Southwest Airlines, JetBlue, AirTran Airways, Skybus Airlines and other low-cost carriers began to represent a serious challenge to the so-called "legacy airlines", as did their low-cost counterparts in many other countries. Their commercial viability represented a serious competitive threat to the legacy carriers. However, of these, ATA and Skybus have since ceased operations.
Increasingly since 1978, US airlines have been reincorporated and spun off by newly created and internally led management companies, and thus becoming nothing more than operating units and subsidiaries with limited financially decisive control. Among some of these holding companies and parent companies which are relatively well known, are the UAL Corporation, along with the AMR Corporation, among a long list of airline holding companies sometime recognized worldwide. Less recognized are the private-equity firms which often seize managerial, financial, and board of directors control of distressed airline companies by temporarily investing large sums of capital in air carriers, to rescheme an airlines assets into a profitable organization or liquidating an air carrier of their profitable and worthwhile routes and business operations. | Airline | Wikipedia | 440 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
Thus the last 50 years of the airline industry have varied from reasonably profitable, to devastatingly depressed. As the first major market to deregulate the industry in 1978, U.S. airlines have experienced more turbulence than almost any other country or region. In fact, no U.S. legacy carrier survived bankruptcy-free. Among the outspoken critics of deregulation, former CEO of American Airlines, Robert Crandall has publicly stated: "Chapter 11 bankruptcy protection filing shows airline industry deregulation was a mistake."
Bailout
Congress passed the Air Transportation Safety and System Stabilization Act (P.L. 107–42) in response to a severe liquidity crisis facing the already-troubled airline industry in the aftermath of the September 11 attacks. Through the ATSB Congress sought to provide cash infusions to carriers for both the cost of the four-day federal shutdown of the airlines and the incremental losses incurred through December 31, 2001, as a result of the terrorist attacks. This resulted in the first government bailout of the 21st century. Between 2000 and 2005 US airlines lost $30 billion with wage cuts of over $15 billion and 100,000 employees laid off.
In recognition of the essential national economic role of a healthy aviation system, Congress authorized partial compensation of up to $5 billion in cash subject to review by the U.S. Department of Transportation and up to $10 billion in loan guarantees subject to review by a newly created Air Transportation Stabilization Board (ATSB). The applications to DOT for reimbursements were subjected to rigorous multi-year reviews not only by DOT program personnel but also by the Government Accountability Office and the DOT Inspector General.
Ultimately, the federal government provided $4.6 billion in one-time, subject-to-income-tax cash payments to 427 U.S. air carriers, with no provision for repayment, essentially a gift from the taxpayers. (Passenger carriers operating scheduled service received approximately $4 billion, subject to tax.) In addition, the ATSB approved loan guarantees to six airlines totaling approximately $1.6 billion. Data from the U.S. Treasury Department show that the government recouped the $1.6 billion and a profit of $339 million from the fees, interest and purchase of discounted airline stock associated with loan guarantees.
The three largest major carriers and Southwest Airlines control 70% of the U.S. passenger market.
Asia | Airline | Wikipedia | 492 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
Although Philippine Airlines (PAL) was officially founded on February 26, 1941, its license to operate as an airliner was derived from merged Philippine Aerial Taxi Company (PATCO) established by mining magnate Emmanuel N. Bachrach on 3 December 1930, making it Asia's oldest scheduled carrier still in operation. Commercial air service commenced three weeks later from Manila to Baguio, making it Asia's first airline route. Bachrach's death in 1937 paved the way for its eventual merger with Philippine Airlines in March 1941 and made it Asia's oldest airline. It is also the oldest airline in Asia still operating under its current name. Bachrach's majority share in PATCO was bought by beer magnate Andres R. Soriano in 1939 upon the advice of General Douglas MacArthur and later merged with newly formed Philippine Airlines with PAL as the surviving entity. Soriano has controlling interest in both airlines before the merger. PAL restarted service on 15 March 1941, with a single Beech Model 18 NPC-54 aircraft, which started its daily services between Manila (from Nielson Field) and Baguio, later to expand with larger aircraft such as the DC-3 and Vickers Viscount.
In Japan, Japan Air Transport was established in 1928 as the national flag carrier. Upon the completion of Haneda Airport in 1931, it became the airline's hub. The airline initially operated domestic routes such as Tokyo–Osaka and Osaka–Fukuoka. In September 1929, it opened its first overseas route, which connected Fukuoka to Dalian in the Kwantung Leased Territory via Seoul and Pyongyang in Japanese Korea. After Japan established the puppet state of Manchukuo, the airline opened routes to major cities within this territory. The company was reorganised as Japan Airways in 1938. During the Second World War, it operated routes to various Japanese-occupied territories and Thailand. The company was dissolved immediately after the war, as civil aviation was prohibited by the Allied Occupation Forces. Civil aviation in Japan did not resume until the founding of Japan Airlines in 1951. | Airline | Wikipedia | 416 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
Cathay Pacific was one of the first airlines to be launched among the other Asian countries in 1946. The license to operate as an airliner was granted by the federal government body after reviewing the necessity at the national assembly. The Hanjin occupies the largest ownership of Korean Air as well as few low-budget airlines as of now. Korean Air is one of the four founders of SkyTeam, which was established in 2000. Asiana Airlines, launched in 1988, joined Star Alliance in 2003. Korean Air and Asiana Airlines comprise one of the largest combined airline miles and number of passenger served at the regional market of Asian airline industry
India was also one of the first countries to embrace civil aviation. One of the first Asian airline companies was Air India, which was founded as Tata Airlines in 1932, a division of Tata Sons Ltd. (now Tata Group). The airline was founded by India's leading industrialist, JRD Tata. On 15 October 1932, J. R. D. Tata himself flew a single engined De Havilland Puss Moth carrying air mail (postal mail of Imperial Airways) from Karachi to Bombay via Ahmedabad. The aircraft continued to Madras via Bellary piloted by Royal Air Force pilot Nevill Vintcent. Tata Airlines was also one of the world's first major airlines which began its operations without any support from the Government.
With the outbreak of World War II, the airline presence in Asia came to a relative halt, with many new flag carriers donating their aircraft for military aid and other uses. Following the end of the war in 1945, regular commercial service was restored in India and Tata Airlines became a public limited company on 29 July 1946, under the name Air India. After the independence of India, 49% of the airline was acquired by the Government of India. In return, the airline was granted status to operate international services from India as the designated flag carrier under the name Air India International.
On 31 July 1946, a chartered Philippine Airlines (PAL) DC-4 ferried 40 American servicemen to Oakland, California, from Nielson Airport in Makati with stops in Guam, Wake Island, Johnston Atoll and Honolulu, Hawaii, making PAL the first Asian airline to cross the Pacific Ocean. A regular service between Manila and San Francisco was started in December. It was during this year that the airline was designated as the flag carrier of Philippines. | Airline | Wikipedia | 477 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
During the era of decolonization, newly born Asian countries started to embrace air transport. Among the first Asian carriers during the era were Cathay Pacific of Hong Kong (founded in September 1946), Orient Airways (later Pakistan International Airlines; founded in October 1946), Air Ceylon (later SriLankan Airlines; founded in 1947), Malayan Airways Limited in 1947 (later Singapore and Malaysia Airlines), El Al in Israel in 1948, Garuda Indonesia in 1949, Thai Airways in 1960, and Korean National Airlines in 1947.
Latin America and Caribbean
Among the first countries to have regular airlines in Latin America and the Caribbean were Bolivia with Lloyd Aéreo Boliviano, Cuba with Cubana de Aviación, Colombia with Avianca (the first airline established in the Americas), Argentina with Aerolíneas Argentinas, Chile with LAN Chile (today LATAM Airlines), Brazil with Varig, the Dominican Republic with Dominicana de Aviación, Mexico with Mexicana de Aviación, Trinidad and Tobago with BWIA West Indies Airways (today Caribbean Airlines), Venezuela with Aeropostal, Puerto Rico with Puertorriquena; and TACA based in El Salvador and representing several airlines of Central America (Costa Rica, Guatemala, Honduras and Nicaragua). All the previous airlines started regular operations well before World War II. Puerto Rican commercial airlines such as Prinair, Oceanair, Fina Air and Vieques Air Link came much after the second world war, as did several others from other countries like Mexico's Interjet and Volaris, Venezuela's Aserca Airlines and others.
The air travel market has evolved rapidly over recent years in Latin America. Some industry estimates indicated in 2011 that over 2,000 new aircraft will begin service over the next five years in this region.
These airlines serve domestic flights within their countries, as well as connections within Latin America and also overseas flights to North America, Europe, Australia, and Asia. | Airline | Wikipedia | 398 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
Only five airline groups – Avianca, Panama's Copa, Mexico's Volaris, the Irelandia group and LATAM Airlines – have international subsidiaries and cover many destinations within the Americas as well as major hubs in other continents. LATAM with Chile as the central operation along with Peru, Ecuador, Colombia, Brazil and Argentina and formerly with some operations in the Dominican Republic. The Avianca group has its main operation in Colombia based around the hub in Bogotá, Colombia, as well as subsidiaries in various Latin American countries with hubs in San Salvador, El Salvador, as well as Lima, Peru, with a smaller operation in Ecuador. Copa has subsidiaries Copa Airlines Colombia and Wingo, both in Colombia, while Volaris of Mexico has Volaris Costa Rica and Volaris El Salvador, and the Irelandia group formerly included Viva Aerobus of Mexico; it formerly included Viva Colombia and Viva Air Peru.
Regulation
National
Many countries have national airlines that the government owns and operates. Fully private airlines are subject to much government regulation for economic, political, and safety concerns. For instance, governments often intervene to halt airline labor actions to protect the free flow of people, communications, and goods between different regions without compromising safety.
The United States, Australia, and to a lesser extent Brazil, Mexico, India, the United Kingdom, and Japan have "deregulated" their airlines. In the past, these governments dictated airfares, route networks, and other operational requirements for each airline. Since deregulation, airlines have been largely free to negotiate their own operating arrangements with different airports, enter and exit routes easily, and to levy airfares and supply flights according to market demand. The entry barriers for new airlines are lower in a deregulated market, and so the U.S. has seen hundreds of airlines start up (sometimes for only a brief operating period). This has produced far greater competition than before deregulation in most markets. The added competition, together with pricing freedom, means that new entrants often take market share with highly reduced rates that, to a limited degree, full service airlines must match. This is a major constraint on profitability for established carriers, which tend to have a higher cost base.
As a result, profitability in a deregulated market is uneven for most airlines. These forces have caused some major airlines to go out of business, in addition to most of the poorly established new entrants. | Airline | Wikipedia | 496 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
In the United States, the airline industry is dominated by four large firms. Because of industry consolidation, after fuel prices dropped considerably in 2015, very little of the savings were passed on to consumers.
International
Groups such as the International Civil Aviation Organization establish worldwide standards for safety and other vital concerns. Most international air traffic is regulated by bilateral agreements between countries, which designate specific carriers to operate on specific routes. The model of such an agreement was the Bermuda Agreement between the US and UK following World War II, which designated airports to be used for transatlantic flights and gave each government the authority to nominate carriers to operate routes.
Bilateral agreements are based on the "freedoms of the air", a group of generalized traffic rights ranging from the freedom to overfly a country to the freedom to provide domestic flights within a country (a very rarely granted right known as cabotage). Most agreements permit airlines to fly from their home country to designated airports in the other country: some also extend the freedom to provide continuing service to a third country, or to another destination in the other country while carrying passengers from overseas.
In the 1990s, "open skies" agreements became more common. These agreements take many of these regulatory powers from state governments and open up international routes to further competition. Open skies agreements have met some criticism, particularly within the European Union, whose airlines would be at a comparative disadvantage with the United States' because of cabotage restrictions.
Economy
In 2017, 4.1 billion passengers have been carried by airlines in 41.9 million commercial scheduled flights (an average payload of passengers), for 7.75 trillion passenger kilometres (an average trip of km) over 45,091 airline routes served globally. In 2016, air transport generated $704.4 billion of revenue in 2016, employed 10.2 million workers, supported 65.5 million jobs and $2.7 trillion of economic activity: 3.6% of the global GDP.
In July 2016, the total weekly airline capacity was 181.1 billion Available Seat Kilometers (+6.9% compared to July 2015): 57.6bn in Asia-Pacific, 47.7bn in Europe, 46.2bn in North America, 12.2bn in Middle East, 12.0bn in Latin America and 5.4bn in Africa.
Costs | Airline | Wikipedia | 466 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
Airlines have substantial fixed and operating costs to establish and maintain air services: labor, fuel, airplanes, engines, spares and parts, IT services and networks, airport equipment, airport handling services, booking commissions, advertising, catering, training, aviation insurance and other costs. Thus all but a small percentage of the income from ticket sales is paid out to a wide variety of external providers or internal cost centers.
Moreover, the industry is structured so that airlines often act as tax collectors. Airline fuel is untaxed because of a series of treaties existing between countries. Ticket prices include a number of fees, taxes and surcharges beyond the control of airlines. Airlines are also responsible for enforcing government regulations. If airlines carry passengers without proper documentation on an international flight, they are responsible for returning them back to the original country.
Analysis of the 1992–1996 period shows that every player in the air transport chain is far more profitable than the airlines, who collect and pass through fees and revenues to them from ticket sales. While airlines as a whole earned 6% return on capital employed (2–3.5% less than the cost of capital), airports earned 10%, catering companies 10–13%, handling companies 11–14%, aircraft lessors 15%, aircraft manufacturers 16%, and global distribution companies more than 30%.
There has been continuing cost competition from low cost airlines. Many companies emulate Southwest Airlines in various respects. The lines between full-service and low-cost airlines have become blurred – e.g., with most "full service" airlines introducing baggage check fees despite Southwest not doing so.
Many airlines in the U.S. and elsewhere have experienced business difficulty. U.S. airlines that have declared Chapter 11 bankruptcy since 1990 have included American Airlines, Continental Airlines (twice), Delta Air Lines, Northwest Airlines, Pan Am, United Airlines and US Airways (twice).
Where an airline has established an engineering base at an airport, then there may be considerable economic advantages in using that same airport as a preferred focus (or "hub") for its scheduled flights.
Fuel hedging is a contractual tool used by transportation companies like airlines to reduce their exposure to volatile and potentially rising fuel costs. Several low-cost carriers such as Southwest Airlines adopt this practice. Southwest is credited with maintaining strong business profits between 1999 and the early 2000s due to its fuel hedging policy. Many other airlines are replicating Southwest's hedging policy to control their fuel costs. | Airline | Wikipedia | 505 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
Operating costs for US major airlines are primarily aircraft operating expense including jet fuel, aircraft maintenance, depreciation and aircrew for 44%, servicing expense for 29% (traffic 11%, passenger 11% and aircraft 7%), 14% for reservations and sales and 13% for overheads (administration 6% and advertising 2%). An average US major Boeing 757-200 flies stages 11.3 block hours per day and costs $2,550 per block hour: $923 of ownership, $590 of maintenance, $548 of fuel and $489 of crew; or $13.34 per 186 seats per block hour. For a Boeing 737-500, a low-cost carrier like Southwest have lower operating costs at $1,526 than a full service one like United at $2,974, and higher productivity with 399,746 ASM per day against 264,284, resulting in a unit cost of $cts/ASM against $cts/ASM.
McKinsey observes that "newer technology, larger aircraft, and increasingly efficient operations continually drive down the cost of running an airline", from nearly 40 US cents per ASK at the beginning of the jet age, to just above 10 cents since 2000. Those improvements were passed onto the customer due to high competition: fares have been falling throughout the history of airlines.
Revenue
Airlines assign prices to their services in an attempt to maximize profitability. The pricing of airline tickets has become increasingly complicated over the years and is now largely determined by computerized yield management systems.
Because of the complications in scheduling flights and maintaining profitability, airlines have many loopholes that can be used by the knowledgeable traveler. Many of these airfare secrets are becoming more and more known to the general public, so airlines are forced to make constant adjustments.
Most airlines use differentiated pricing, a form of price discrimination, to sell air services at varying prices simultaneously to different segments. Factors influencing the price include the days remaining until departure, the booked load factor, the forecast of total demand by price point, competitive pricing in force, and variations by day of week of departure and by time of day. Carriers often accomplish this by dividing each cabin of the aircraft (first, business and economy) into a number of travel classes for pricing purposes. | Airline | Wikipedia | 469 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
A complicating factor is that of origin-destination control ("O&D control"). Someone purchasing a ticket from Melbourne to Sydney (as an example) for A$200 is competing with someone else who wants to fly Melbourne to Los Angeles through Sydney on the same flight, and who is willing to pay A$1400. Should the airline prefer the $1400 passenger, or the $200 passenger plus a possible Sydney-Los Angeles passenger willing to pay $1300? Airlines have to make hundreds of thousands of similar pricing decisions daily.
The advent of advanced computerized reservations systems in the late 1970s, most notably Sabre, allowed airlines to easily perform cost-benefit analyses on different pricing structures, leading to almost perfect price discrimination in some cases (that is, filling each seat on an aircraft at the highest price that can be charged without driving the consumer elsewhere).
The intense nature of airfare pricing has led to the term "fare war" to describe efforts by airlines to undercut other airlines on competitive routes. Through computers, new airfares can be published quickly and efficiently to the airlines' sales channels. For this purpose the airlines use the Airline Tariff Publishing Company (ATPCO), who distribute latest fares for more than 500 airlines to Computer Reservation Systems across the world.
The extent of these pricing phenomena is strongest in "legacy" carriers. In contrast, low fare carriers usually offer pre-announced and simplified price structure, and sometimes quote prices for each leg of a trip separately.
Computers also allow airlines to predict, with some accuracy, how many passengers will actually fly after making a reservation to fly. This allows airlines to overbook their flights enough to fill the aircraft while accounting for "no-shows", but not enough (in most cases) to force paying passengers off the aircraft for lack of seats, stimulative pricing for low demand flights coupled with overbooking on high demand flights can help reduce this figure. This is especially crucial during tough economic times as airlines undertake massive cuts to ticket prices to retain demand.
Over January/February 2018, the cheapest airline surveyed by price comparator rome2rio was now-defunct Tigerair Australia with $0.06/km followed by AirAsia X with $0.07/km, while the most expensive was Charterlines, Inc. with $1.26/km followed by Buddha Air with $1.18/km. | Airline | Wikipedia | 485 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
For the IATA, the global airline industry revenue was $754 billion in 2017 for a $38.4 billion collective profit, and should rise by 10.7% to $834 billion in 2018 for a $33.8 billion profit forecast, down by 12% due to rising jet fuel and labor costs.
The demand for air transport will be less elastic for longer flights than for shorter flights, and more elastic for leisure travel than for business travel.
Airlines often have a strong seasonality, with traffic low in winter and peaking in summer. In Europe the most extreme market are the Greek islands with July/August having more than ten times the winter traffic, as Jet2 is the most seasonal among low-cost carriers with July having seven times the January traffic, whereas legacy carriers are much less with only 85/115% variability.
Assets and financing
Airline financing is quite complex, since airlines are highly leveraged operations. Not only must they purchase (or lease) new airliner bodies and engines regularly, they must make major long-term fleet decisions with the goal of meeting the demands of their markets while producing a fleet that is relatively economical to operate and maintain; comparably Southwest Airlines and their reliance on a single airplane type (the Boeing 737 and derivatives), with the now defunct Eastern Air Lines which operated 17 different aircraft types, each with varying pilot, engine, maintenance, and support needs.
A second financial issue is that of hedging oil and fuel purchases, which are usually second only to labor in its relative cost to the company. However, with the current high fuel prices it has become the largest cost to an airline. Legacy airlines, compared with new entrants, have been hit harder by rising fuel prices partly due to the running of older, less fuel efficient aircraft. While hedging instruments can be expensive, they can easily pay for themselves many times over in periods of increasing fuel costs, such as in the 2000–2005 period.
In view of the congestion apparent at many international airports, the ownership of slots at certain airports (the right to take-off or land an aircraft at a particular time of day or night) has become a significant tradable asset for many airlines. Clearly take-off slots at popular times of the day can be critical in attracting the more profitable business traveler to a given airline's flight and in establishing a competitive advantage against a competing airline. | Airline | Wikipedia | 484 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
If a particular city has two or more airports, market forces will tend to attract the less profitable routes, or those on which competition is weakest, to the less congested airport, where slots are likely to be more available and therefore cheaper. For example, Reagan National Airport attracts profitable routes due partly to its congestion, leaving less-profitable routes to Baltimore-Washington International Airport and Dulles International Airport.
Other factors, such as surface transport facilities and onward connections, will also affect the relative appeal of different airports and some long-distance flights may need to operate from the one with the longest runway. For example, LaGuardia Airport is the preferred airport for most of Manhattan due to its proximity, while long-distance routes must use John F. Kennedy International Airport's longer runways.
Airline alliances
The first airline alliance was formed in the 1930s when Pan Am and its subsidiary, Panair do Brasil, agreed to codeshare routes in Latin America when they overlapped with each other.
Codesharing involves one airline selling tickets for another airline's flights under its own airline code. An early example of this was Japan Airlines' (JAL) codesharing partnership with Aeroflot in the 1960s on Tokyo–Moscow flights; Aeroflot operated the flights using Aeroflot aircraft, but JAL sold tickets for the flights as if they were JAL flights. Another example was the Austrian–Sabena partnership on the Vienna–Brussels–New York/JFK route during the late '60s, using a Sabena Boeing 707 with Austrian livery.
Since airline reservation requests are often made by city-pair (such as "show me flights from Chicago to Düsseldorf"), an airline that can codeshare with another airline for a variety of routes might be able to be listed as indeed offering a Chicago–Düsseldorf flight. The passenger is advised however, that airline no. 1 operates the flight from say Chicago to Amsterdam (for example), and airline no. 2 operates the continuing flight (on a different airplane, sometimes from another terminal) to Düsseldorf. Thus the primary rationale for code sharing is to expand one's service offerings in city-pair terms to increase sales. | Airline | Wikipedia | 443 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
A more recent development is the airline alliance, which became prevalent in the late 1990s. These alliances can act as virtual mergers to get around government restrictions. The largest are Star Alliance, SkyTeam and Oneworld, and these accounted for over 60% of global commercial air traffic . Alliances of airlines coordinate their passenger service programs (such as lounges and frequent-flyer programs), offer special interline tickets and often engage in extensive codesharing (sometimes systemwide). These are increasingly integrated business combinations—sometimes including cross-equity arrangements—in which products, service standards, schedules, and airport facilities are standardized and combined for higher efficiency. One of the first airlines to start an alliance with another airline was KLM, who partnered with Northwest Airlines. Both airlines later entered the SkyTeam alliance after the fusion of KLM and Air France in 2004.
Often the companies combine IT operations, or purchase fuel and aircraft as a bloc to achieve higher bargaining power. However, the alliances have been most successful at purchasing invisible supplies and services, such as fuel. Airlines usually prefer to purchase items visible to their passengers to differentiate themselves from local competitors. If an airline's main domestic competitor flies Boeing airliners, then the airline may prefer to use Airbus aircraft regardless of what the rest of the alliance chooses.
Largest airlines
The world's largest airlines can be defined in several ways. , American Airlines Group was the largest by fleet size, passengers carried and revenue passenger mile. Delta Air Lines was the largest by revenue, assets value and market capitalization. Lufthansa Group was the largest by number of employees, FedEx Express by freight tonne-kilometres, Turkish Airlines by number of countries served and UPS Airlines by number of destinations served (though United Airlines was the largest passenger airline by number of destinations served).
State support
Historically, air travel has survived largely through state support, whether in the form of equity or subsidies. The airline industry as a whole has made a cumulative loss during its 100-year history. | Airline | Wikipedia | 404 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
One argument is that positive externalities, such as higher growth due to global mobility, outweigh the microeconomic losses and justify continuing government intervention. A historically high level of government intervention in the airline industry can be seen as part of a wider political consensus on strategic forms of transport, such as highways and railways, both of which receive public funding in most parts of the world. Although many countries continue to operate state-owned or parastatal airlines, many large airlines today are privately owned and are therefore governed by microeconomic principles to maximize shareholder profit.
In December 1991, the collapse of Pan Am, an airline often credited for shaping the international airline industry, highlighted the financial complexities faced by major airline companies.
Following the 1978 deregulation, U.S. carriers did not manage to make an aggregate profit for 12 years in 31, including four years where combined losses amounted to $10 billion, but rebounded with eight consecutive years of profits since 2010, including its four with over $10 billion profits. They drop loss-making routes, avoid fare wars and market share battles, limit capacity growth, add hub feed with regional jets to increase their profitability. They change schedules to create more connections, buy used aircraft, reduce international frequencies and leverage partnerships to optimize capacities and benefit from overseas connectivity.
Environment
Aircraft engines emit noise pollution, gases and particulate emissions, and contribute to global dimming.
Growth of the industry in recent years raised a number of ecological questions.
Domestic air transport grew in China at 15.5 percent annually from 2001 to 2006. The rate of air travel globally increased at 3.7 percent per year over the same time. In the EU greenhouse gas emissions from aviation increased by 87% between 1990 and 2006. However it must be compared with the flights increase, only in UK, between 1990 and 2006 terminal passengers increased from 100 000 thousands to 250 000 thousands., according to AEA reports every year, 750 million passengers travel by European airlines, which also share 40% of merchandise value in and out of Europe. Without even pressure from "green activists", targeting lower ticket prices, generally, airlines do what is possible to cut the fuel consumption (and gas emissions connected therewith). Further, according to some reports, it can be concluded that the last piston-powered aircraft were as fuel-efficient as the average jet in 2005. | Airline | Wikipedia | 477 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
Despite continuing efficiency improvements from the major aircraft manufacturers, the expanding demand for global air travel has resulted in growing greenhouse gas (GHG) emissions. Currently, the aviation sector, including US domestic and global international travel, make approximately 1.6 percent of global anthropogenic GHG emissions per annum. North America accounts for nearly 40 percent of the world's GHG emissions from aviation fuel use.
emissions from the jet fuel burned per passenger on an average airline flight is about 353 kilograms (776 pounds). Loss of natural habitat potential associated with the jet fuel burned per passenger on a airline flight is estimated to be 250 square meters (2700 square feet).
In the context of climate change and peak oil, there is a debate about possible taxation of air travel and the inclusion of aviation in an emissions trading scheme, with a view to ensuring that the total external costs of aviation are taken into account.
The airline industry is responsible for about 11 percent of greenhouse gases emitted by the U.S. transportation sector. Boeing estimates that biofuels could reduce flight-related greenhouse-gas emissions by 60 to 80 percent. The solution would be blending algae fuels with existing jet fuel:
Boeing and Air New Zealand are collaborating with leading Brazilian biofuel maker Tecbio, New Zealand's Aquaflow Bionomic and other jet biofuel developers around the world.
Virgin Atlantic and Virgin Green Fund are looking into the technology as part of a biofuel initiative.
KLM has made the first commercial flight with biofuel in 2009.
There are projects on electric aircraft, and some of which are fully operational as of 2013.
Call signs
Each operator of a scheduled or charter flight uses an airline call sign when communicating with airports or air traffic control. Most of these call-signs are derived from the airline's trade name, but for reasons of history, marketing, or the need to reduce ambiguity in spoken English (so that pilots do not mistakenly make navigational decisions based on instructions issued to a different aircraft), some airlines and air forces use call-signs less obviously connected with their trading name. For example, British Airways uses a Speedbird call-sign, named after the logo of one of its predecessors, BOAC, while SkyEurope used Relax.
Personnel | Airline | Wikipedia | 459 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
The various types of airline personnel include flight crew, responsible for the operation of the aircraft. Flight crew members include: pilots (captain and first officer: some older aircraft also required a flight engineer and/or a navigator); flight attendants (led by a purser on larger aircraft); In-flight security personnel on some airlines (most notably El Al)
Groundcrew, responsible for operations at airports, include Aerospace and avionics engineers responsible for certifying the aircraft for flight and management of aircraft maintenance; Aerospace engineers, responsible for airframe, powerplant and electrical systems maintenance; Avionics engineers responsible for avionics and instruments maintenance; Airframe and powerplant technicians; Electric System technicians, responsible for maintenance of electrical systems; Flight dispatchers; Baggage handlers; Ramp Agents; Remote centralized weight and balancing; Gate agents; Ticket agents; Passenger service agents (such as airline lounge employees); Reservation agents, usually (but not always) at facilities outside the airport; Crew schedulers.
Airlines follow a corporate structure where each broad area of operations (such as maintenance, flight operations (including flight safety), and passenger service) is supervised by a vice president. Larger airlines often appoint vice presidents to oversee each of the airline's hubs as well. Airlines employ lawyers to deal with regulatory procedures and other administrative tasks.
Trends
The pattern of ownership has been privatized since the mid-1980s, that is, the ownership has gradually changed from governments to private and individual sectors or organizations. This occurs as regulators permit greater freedom and non-government ownership, in steps that are usually decades apart. This pattern is not seen for all airlines in all regions. Many major airlines operating between the 1940s and 1980s were government-owned or government-established. However, most airlines from the earliest days of air travel in the 1920s and 1930s were personal businesses. | Airline | Wikipedia | 373 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
Growth rates are not consistent in all regions, but countries with a deregulated airline industry have more competition and greater pricing freedom. This results in lower fares and sometimes dramatic spurts in traffic growth. The U.S., Australia, Canada, Japan, Brazil, India and other markets exhibit this trend. The industry has been observed to be cyclical in its financial performance. Four or five years of poor earnings precede five or six years of improvement. But profitability even in the good years is generally low, in the range of 2–3% net profit after interest and tax. In times of profit, airlines lease new generations of airplanes and upgrade services in response to higher demand. Since 1980, the industry has not earned back the cost of capital during the best of times. Conversely, in bad times losses can be dramatically worse. Warren Buffett in 1999 said "the money that had been made since the dawn of aviation by all of this country's airline companies was zero. Absolutely zero."
As in many mature industries, consolidation is a trend. Airline groupings may consist of limited bilateral partnerships, long-term, multi-faceted alliances between carriers, equity arrangements, mergers, or takeovers. Since governments often restrict ownership and merger between companies in different countries, most consolidation takes place within a country. In the U.S., over 200 airlines have merged, been taken over, or gone out of business since the Airline Deregulation Act in 1978. Many international airline managers are lobbying their governments to permit greater consolidation to achieve higher economy and efficiency.
Types
There are several types of passenger airlines, mainly:
Mainline airlines operate flights by the airline's main operating unit, rather than by regional affiliates or subsidiaries.
Regional airlines, non-"mainline" airlines that operate regional aircraft; regionals typically operate over shorter non-intercontinental distances, often as feeder services for legacy mainline networks.
Low-cost carriers, giving a "basic", "no-frills" and perceived inexpensive service.
Business class airline, an airline aimed at the business traveler, featuring all business class seating and amenities.
Charter airlines, operating outside regular schedule intervals.
Flag carriers, the historically nationally owned airlines that were considered representative of the country overseas.
Legacy carriers, US carriers that predate the Airline Deregulation Act of 1978.
Major airlines of the United States, airlines with at least $1 billion in revenues.
In addition, there are several cargo-only airlines. | Airline | Wikipedia | 497 | 1942 | https://en.wikipedia.org/wiki/Airline | Technology | Aviation | null |
Apparent magnitude () is a measure of the brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction of the object's light caused by interstellar dust along the line of sight to the observer.
Unless stated otherwise, the word magnitude in astronomy usually refers to a celestial object's apparent magnitude. The magnitude scale likely dates to before the ancient Roman astronomer Claudius Ptolemy, whose star catalog popularized the system by listing stars from 1st magnitude (brightest) to 6th magnitude (dimmest). The modern scale was mathematically defined to closely match this historical system by Norman Pogson in 1856.
The scale is reverse logarithmic: the brighter an object is, the lower its magnitude number. A difference of 1.0 in magnitude corresponds to the brightness ratio of , or about 2.512. For example, a magnitude 2.0 star is 2.512 times as bright as a magnitude 3.0 star, 6.31 times as magnitude 4.0, and 100 times magnitude 7.0.
The brightest astronomical objects have negative apparent magnitudes: for example, Venus at −4.2 or Sirius at −1.46. The faintest stars visible with the naked eye on the darkest night have apparent magnitudes of about +6.5, though this varies depending on a person's eyesight and with altitude and atmospheric conditions. The apparent magnitudes of known objects range from the Sun at −26.832 to objects in deep Hubble Space Telescope images of magnitude +31.5.
The measurement of apparent magnitude is called photometry. Photometric measurements are made in the ultraviolet, visible, or infrared wavelength bands using standard passband filters belonging to photometric systems such as the UBV system or the Strömgren uvbyβ system. Measurement in the V-band may be referred to as the apparent visual magnitude.
Absolute magnitude is a related quantity which measures the luminosity that a celestial object emits, rather than its apparent brightness when observed, and is expressed on the same reverse logarithmic scale. Absolute magnitude is defined as the apparent magnitude that a star or object would have if it were observed from a distance of . Therefore, it is of greater use in stellar astrophysics since it refers to a property of a star regardless of how close it is to Earth. But in observational astronomy and popular stargazing, references to "magnitude" are understood to mean apparent magnitude. | Apparent magnitude | Wikipedia | 509 | 1962 | https://en.wikipedia.org/wiki/Apparent%20magnitude | Physical sciences | Basics | Astronomy |
Amateur astronomers commonly express the darkness of the sky in terms of limiting magnitude, i.e. the apparent magnitude of the faintest star they can see with the naked eye. This can be useful as a way of monitoring the spread of light pollution.
Apparent magnitude is technically a measure of illuminance, which can also be measured in photometric units such as lux.
History
The scale used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six magnitudes. The brightest stars in the night sky were said to be of first magnitude ( = 1), whereas the faintest were of sixth magnitude ( = 6), which is the limit of human visual perception (without the aid of a telescope). Each grade of magnitude was considered twice the brightness of the following grade (a logarithmic scale), although that ratio was subjective as no photodetectors existed. This rather crude scale for the brightness of stars was popularized by Ptolemy in his Almagest and is generally believed to have originated with Hipparchus. This cannot be proved or disproved because Hipparchus's original star catalogue is lost. The only preserved text by Hipparchus himself (a commentary to Aratus) clearly documents that he did not have a system to describe brightness with numbers: He always uses terms like "big" or "small", "bright" or "faint" or even descriptions such as "visible at full moon".
In 1856, Norman Robert Pogson formalized the system by defining a first magnitude star as a star that is 100 times as bright as a sixth-magnitude star, thereby establishing the logarithmic scale still in use today. This implies that a star of magnitude is about 2.512 times as bright as a star of magnitude . This figure, the fifth root of 100, became known as Pogson's Ratio. The 1884 Harvard Photometry and 1886 Potsdamer Duchmusterung star catalogs popularized Pogson's ratio, and eventually it became a de facto standard in modern astronomy to describe differences in brightness. | Apparent magnitude | Wikipedia | 426 | 1962 | https://en.wikipedia.org/wiki/Apparent%20magnitude | Physical sciences | Basics | Astronomy |
Defining and calibrating what magnitude 0.0 means is difficult, and different types of measurements which detect different kinds of light (possibly by using filters) have different zero points. Pogson's original 1856 paper defined magnitude 6.0 to be the faintest star the unaided eye can see, but the true limit for faintest possible visible star varies depending on the atmosphere and how high a star is in the sky. The Harvard Photometry used an average of 100 stars close to Polaris to define magnitude 5.0. Later, the Johnson UVB photometric system defined multiple types of photometric measurements with different filters, where magnitude 0.0 for each filter is defined to be the average of six stars with the same spectral type as Vega. This was done so the color index of these stars would be 0. Although this system is often called "Vega normalized", Vega is slightly dimmer than the six-star average used to define magnitude 0.0, meaning Vega's magnitude is normalized to 0.03 by definition.
With the modern magnitude systems, brightness is described using Pogson's ratio. In practice, magnitude numbers rarely go above 30 before stars become too faint to detect. While Vega is close to magnitude 0, there are four brighter stars in the night sky at visible wavelengths (and more at infrared wavelengths) as well as the bright planets Venus, Mars, and Jupiter, and since brighter means smaller magnitude, these must be described by negative magnitudes. For example, Sirius, the brightest star of the celestial sphere, has a magnitude of −1.4 in the visible. Negative magnitudes for other very bright astronomical objects can be found in the table below.
Astronomers have developed other photometric zero point systems as alternatives to Vega normalized systems. The most widely used is the AB magnitude system, in which photometric zero points are based on a hypothetical reference spectrum having constant flux per unit frequency interval, rather than using a stellar spectrum or blackbody curve as the reference. The AB magnitude zero point is defined such that an object's AB and Vega-based magnitudes will be approximately equal in the V filter band. However, the AB magnitude system is defined assuming an idealized detector measuring only one wavelength of light, while real detectors accept energy from a range of wavelengths.
Measurement | Apparent magnitude | Wikipedia | 469 | 1962 | https://en.wikipedia.org/wiki/Apparent%20magnitude | Physical sciences | Basics | Astronomy |
Precision measurement of magnitude (photometry) requires calibration of the photographic or (usually) electronic detection apparatus. This generally involves contemporaneous observation, under identical conditions, of standard stars whose magnitude using that spectral filter is accurately known. Moreover, as the amount of light actually received by a telescope is reduced due to transmission through the Earth's atmosphere, the airmasses of the target and calibration stars must be taken into account. Typically one would observe a few different stars of known magnitude which are sufficiently similar. Calibrator stars close in the sky to the target are favoured (to avoid large differences in the atmospheric paths). If those stars have somewhat different zenith angles (altitudes) then a correction factor as a function of airmass can be derived and applied to the airmass at the target's position. Such calibration obtains the brightness as would be observed from above the atmosphere, where apparent magnitude is defined.
The apparent magnitude scale in astronomy reflects the received power of stars and not their amplitude. Newcomers should consider using the relative brightness measure in astrophotography to adjust exposure times between stars. Apparent magnitude also integrates over the entire object, regardless of its focus, and this needs to be taken into account when scaling exposure times for objects with significant apparent size, like the Sun, Moon and planets. For example, directly scaling the exposure time from the Moon to the Sun works because they are approximately the same size in the sky. However, scaling the exposure from the Moon to Saturn would result in an overexposure if the image of Saturn takes up a smaller area on your sensor than the Moon did (at the same magnification, or more generally, f/#).
Calculations
The dimmer an object appears, the higher the numerical value given to its magnitude, with a difference of 5 magnitudes corresponding to a brightness factor of exactly 100. Therefore, the magnitude , in the spectral band , would be given by
which is more commonly expressed in terms of common (base-10) logarithms as
where is the observed irradiance using spectral filter , and is the reference flux (zero-point) for that photometric filter. Since an increase of 5 magnitudes corresponds to a decrease in brightness by a factor of exactly 100, each magnitude increase implies a decrease in brightness by the factor (Pogson's ratio). Inverting the above formula, a magnitude difference implies a brightness factor of | Apparent magnitude | Wikipedia | 499 | 1962 | https://en.wikipedia.org/wiki/Apparent%20magnitude | Physical sciences | Basics | Astronomy |
Example: Sun and Moon
What is the ratio in brightness between the Sun and the full Moon?
The apparent magnitude of the Sun is −26.832 (brighter), and the mean magnitude of the full moon is −12.74 (dimmer).
Difference in magnitude:
Brightness factor:
The Sun appears to be approximately times as bright as the full Moon.
Magnitude addition
Sometimes one might wish to add brightness. For example, photometry on closely separated double stars may only be able to produce a measurement of their combined light output. To find the combined magnitude of that double star knowing only the magnitudes of the individual components, this can be done by adding the brightness (in linear units) corresponding to each magnitude.
Solving for yields
where is the resulting magnitude after adding the brightnesses referred to by and .
Apparent bolometric magnitude
While magnitude generally refers to a measurement in a particular filter band corresponding to some range of wavelengths, the apparent or absolute bolometric magnitude (mbol) is a measure of an object's apparent or absolute brightness integrated over all wavelengths of the electromagnetic spectrum (also known as the object's irradiance or power, respectively). The zero point of the apparent bolometric magnitude scale is based on the definition that an apparent bolometric magnitude of 0 mag is equivalent to a received irradiance of 2.518×10−8 watts per square metre (W·m−2).
Absolute magnitude
While apparent magnitude is a measure of the brightness of an object as seen by a particular observer, absolute magnitude is a measure of the intrinsic brightness of an object. Flux decreases with distance according to an inverse-square law, so the apparent magnitude of a star depends on both its absolute brightness and its distance (and any extinction). For example, a star at one distance will have the same apparent magnitude as a star four times as bright at twice that distance. In contrast, the intrinsic brightness of an astronomical object, does not depend on the distance of the observer or any extinction.
The absolute magnitude , of a star or astronomical object is defined as the apparent magnitude it would have as seen from a distance of . The absolute magnitude of the Sun is 4.83 in the V band (visual), 4.68 in the Gaia satellite's G band (green) and 5.48 in the B band (blue). | Apparent magnitude | Wikipedia | 484 | 1962 | https://en.wikipedia.org/wiki/Apparent%20magnitude | Physical sciences | Basics | Astronomy |
In the case of a planet or asteroid, the absolute magnitude rather means the apparent magnitude it would have if it were from both the observer and the Sun, and fully illuminated at maximum opposition (a configuration that is only theoretically achievable, with the observer situated on the surface of the Sun).
Standard reference values
The magnitude scale is a reverse logarithmic scale. A common misconception is that the logarithmic nature of the scale is because the human eye itself has a logarithmic response. In Pogson's time this was thought to be true (see Weber–Fechner law), but it is now believed that the response is a power law .
Magnitude is complicated by the fact that light is not monochromatic. The sensitivity of a light detector varies according to the wavelength of the light, and the way it varies depends on the type of light detector. For this reason, it is necessary to specify how the magnitude is measured for the value to be meaningful. For this purpose the UBV system is widely used, in which the magnitude is measured in three different wavelength bands: U (centred at about 350 nm, in the near ultraviolet), B (about 435 nm, in the blue region) and V (about 555 nm, in the middle of the human visual range in daylight). The V band was chosen for spectral purposes and gives magnitudes closely corresponding to those seen by the human eye. When an apparent magnitude is discussed without further qualification, the V magnitude is generally understood.
Because cooler stars, such as red giants and red dwarfs, emit little energy in the blue and UV regions of the spectrum, their power is often under-represented by the UBV scale. Indeed, some L and T class stars have an estimated magnitude of well over 100, because they emit extremely little visible light, but are strongest in infrared.
Measures of magnitude need cautious treatment and it is extremely important to measure like with like. On early 20th century and older orthochromatic (blue-sensitive) photographic film, the relative brightnesses of the blue supergiant Rigel and the red supergiant Betelgeuse irregular variable star (at maximum) are reversed compared to what human eyes perceive, because this archaic film is more sensitive to blue light than it is to red light. Magnitudes obtained from this method are known as photographic magnitudes, and are now considered obsolete. | Apparent magnitude | Wikipedia | 492 | 1962 | https://en.wikipedia.org/wiki/Apparent%20magnitude | Physical sciences | Basics | Astronomy |
For objects within the Milky Way with a given absolute magnitude, 5 is added to the apparent magnitude for every tenfold increase in the distance to the object. For objects at very great distances (far beyond the Milky Way), this relationship must be adjusted for redshifts and for non-Euclidean distance measures due to general relativity.
For planets and other Solar System bodies, the apparent magnitude is derived from its phase curve and the distances to the Sun and observer.
List of apparent magnitudes
Some of the listed magnitudes are approximate. Telescope sensitivity depends on observing time, optical bandpass, and interfering light from scattering and airglow. | Apparent magnitude | Wikipedia | 128 | 1962 | https://en.wikipedia.org/wiki/Apparent%20magnitude | Physical sciences | Basics | Astronomy |
In astronomy, absolute magnitude () is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale; the more luminous (intrinsically bright) an object, the lower its magnitude number. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it were viewed from a distance of exactly , without extinction (or dimming) of its light due to absorption by interstellar matter and cosmic dust. By hypothetically placing all objects at a standard reference distance from the observer, their luminosities can be directly compared among each other on a magnitude scale. For Solar System bodies that shine in reflected light, a different definition of absolute magnitude (H) is used, based on a standard reference distance of one astronomical unit.
Absolute magnitudes of stars generally range from approximately −10 to +20. The absolute magnitudes of galaxies can be much lower (brighter).
The more luminous an object, the smaller the numerical value of its absolute magnitude. A difference of 5 magnitudes between the absolute magnitudes of two objects corresponds to a ratio of 100 in their luminosities, and a difference of n magnitudes in absolute magnitude corresponds to a luminosity ratio of 100n/5. For example, a star of absolute magnitude MV = 3.0 would be 100 times as luminous as a star of absolute magnitude MV = 8.0 as measured in the V filter band. The Sun has absolute magnitude MV = +4.83. Highly luminous objects can have negative absolute magnitudes: for example, the Milky Way galaxy has an absolute B magnitude of about −20.8.
As with all astronomical magnitudes, the absolute magnitude can be specified for different wavelength ranges corresponding to specified filter bands or passbands; for stars a commonly quoted absolute magnitude is the absolute visual magnitude, which uses the visual (V) band of the spectrum (in the UBV photometric system). Absolute magnitudes are denoted by a capital M, with a subscript representing the filter band used for measurement, such as MV for absolute magnitude in the V band.
An object's absolute bolometric magnitude (Mbol) represents its total luminosity over all wavelengths, rather than in a single filter band, as expressed on a logarithmic magnitude scale. To convert from an absolute magnitude in a specific filter band to absolute bolometric magnitude, a bolometric correction (BC) is applied. | Absolute magnitude | Wikipedia | 506 | 1963 | https://en.wikipedia.org/wiki/Absolute%20magnitude | Physical sciences | Basics | Astronomy |
Stars and galaxies
In stellar and galactic astronomy, the standard distance is 10 parsecs (about 32.616 light-years, 308.57 petameters or 308.57 trillion kilometres). A star at 10 parsecs has a parallax of 0.1″ (100 milliarcseconds). Galaxies (and other extended objects) are much larger than 10 parsecs; their light is radiated over an extended patch of sky, and their overall brightness cannot be directly observed from relatively short distances, but the same convention is used. A galaxy's magnitude is defined by measuring all the light radiated over the entire object, treating that integrated brightness as the brightness of a single point-like or star-like source, and computing the magnitude of that point-like source as it would appear if observed at the standard 10 parsecs distance. Consequently, the absolute magnitude of any object equals the apparent magnitude it would have if it were 10 parsecs away.
Some stars visible to the naked eye have such a low absolute magnitude that they would appear bright enough to outshine the planets and cast shadows if they were at 10 parsecs from the Earth. Examples include Rigel (−7.8), Deneb (−8.4), Naos (−6.2), and Betelgeuse (−5.8). For comparison, Sirius has an absolute magnitude of only 1.4, which is still brighter than the Sun, whose absolute visual magnitude is 4.83. The Sun's absolute bolometric magnitude is set arbitrarily, usually at 4.75.
Absolute magnitudes of stars generally range from approximately −10 to +20. The absolute magnitudes of galaxies can be much lower (brighter). For example, the giant elliptical galaxy M87 has an absolute magnitude of −22 (i.e. as bright as about 60,000 stars of magnitude −10). Some active galactic nuclei (quasars like CTA-102) can reach absolute magnitudes in excess of −32, making them the most luminous persistent objects in the observable universe, although these objects can vary in brightness over astronomically short timescales. At the extreme end, the optical afterglow of the gamma ray burst GRB 080319B reached, according to one paper, an absolute r magnitude brighter than −38 for a few tens of seconds.
Apparent magnitude | Absolute magnitude | Wikipedia | 500 | 1963 | https://en.wikipedia.org/wiki/Absolute%20magnitude | Physical sciences | Basics | Astronomy |
The Greek astronomer Hipparchus established a numerical scale to describe the brightness of each star appearing in the sky. The brightest stars in the sky were assigned an apparent magnitude , and the dimmest stars visible to the naked eye are assigned . The difference between them corresponds to a factor of 100 in brightness. For objects within the immediate neighborhood of the Sun, the absolute magnitude and apparent magnitude from any distance (in parsecs, with 1 pc = 3.2616 light-years) are related by
where is the radiant flux measured at distance (in parsecs), the radiant flux measured at distance . Using the common logarithm, the equation can be written as
where it is assumed that extinction from gas and dust is negligible. Typical extinction rates within the Milky Way galaxy are 1 to 2 magnitudes per kiloparsec, when dark clouds are taken into account.
For objects at very large distances (outside the Milky Way) the luminosity distance (distance defined using luminosity measurements) must be used instead of , because the Euclidean approximation is invalid for distant objects. Instead, general relativity must be taken into account. Moreover, the cosmological redshift complicates the relationship between absolute and apparent magnitude, because the radiation observed was shifted into the red range of the spectrum. To compare the magnitudes of very distant objects with those of local objects, a K correction might have to be applied to the magnitudes of the distant objects.
The absolute magnitude can also be written in terms of the apparent magnitude and stellar parallax :
or using apparent magnitude and distance modulus :
Examples
Rigel has a visual magnitude of 0.12 and distance of about 860 light-years:
Vega has a parallax of 0.129″, and an apparent magnitude of 0.03:
The Black Eye Galaxy has a visual magnitude of 9.36 and a distance modulus of 31.06:
Bolometric magnitude
The absolute bolometric magnitude () takes into account electromagnetic radiation at all wavelengths. It includes those unobserved due to instrumental passband, the Earth's atmospheric absorption, and extinction by interstellar dust. It is defined based on the luminosity of the stars. In the case of stars with few observations, it must be computed assuming an effective temperature.
Classically, the difference in bolometric magnitude is related to the luminosity ratio according to:
which makes by inversion: | Absolute magnitude | Wikipedia | 499 | 1963 | https://en.wikipedia.org/wiki/Absolute%20magnitude | Physical sciences | Basics | Astronomy |
where
is the Sun's luminosity (bolometric luminosity)
is the star's luminosity (bolometric luminosity)
is the bolometric magnitude of the Sun
is the bolometric magnitude of the star.
In August 2015, the International Astronomical Union passed Resolution B2 defining the zero points of the absolute and apparent bolometric magnitude scales in SI units for power (watts) and irradiance (W/m2), respectively. Although bolometric magnitudes had been used by astronomers for many decades, there had been systematic differences in the absolute magnitude-luminosity scales presented in various astronomical references, and no international standardization. This led to systematic differences in bolometric corrections scales. Combined with incorrect assumed absolute bolometric magnitudes for the Sun, this could lead to systematic errors in estimated stellar luminosities (and other stellar properties, such as radii or ages, which rely on stellar luminosity to be calculated).
Resolution B2 defines an absolute bolometric magnitude scale where corresponds to luminosity , with the zero point luminosity set such that the Sun (with nominal luminosity ) corresponds to absolute bolometric magnitude . Placing a radiation source (e.g. star) at the standard distance of 10 parsecs, it follows that the zero point of the apparent bolometric magnitude scale corresponds to irradiance . Using the IAU 2015 scale, the nominal total solar irradiance ("solar constant") measured at 1 astronomical unit () corresponds to an apparent bolometric magnitude of the Sun of .
Following Resolution B2, the relation between a star's absolute bolometric magnitude and its luminosity is no longer directly tied to the Sun's (variable) luminosity:
where
is the star's luminosity (bolometric luminosity) in watts
is the zero point luminosity
is the bolometric magnitude of the star
The new IAU absolute magnitude scale permanently disconnects the scale from the variable Sun. However, on this SI power scale, the nominal solar luminosity corresponds closely to , a value that was commonly adopted by astronomers before the 2015 IAU resolution.
The luminosity of the star in watts can be calculated as a function of its absolute bolometric magnitude as:
using the variables as defined previously.
Solar System bodies () | Absolute magnitude | Wikipedia | 506 | 1963 | https://en.wikipedia.org/wiki/Absolute%20magnitude | Physical sciences | Basics | Astronomy |
For planets and asteroids, a definition of absolute magnitude that is more meaningful for non-stellar objects is used. The absolute magnitude, commonly called , is defined as the apparent magnitude that the object would have if it were one astronomical unit (AU) from both the Sun and the observer, and in conditions of ideal solar opposition (an arrangement that is impossible in practice). Because Solar System bodies are illuminated by the Sun, their brightness varies as a function of illumination conditions, described by the phase angle. This relationship is referred to as the phase curve. The absolute magnitude is the brightness at phase angle zero, an arrangement known as opposition, from a distance of one AU.
Apparent magnitude
The absolute magnitude can be used to calculate the apparent magnitude of a body. For an object reflecting sunlight, and are connected by the relation
where is the phase angle, the angle between the body-Sun and body–observer lines. is the phase integral (the integration of reflected light; a number in the 0 to 1 range).
By the law of cosines, we have:
Distances:
is the distance between the body and the observer
is the distance between the body and the Sun
is the distance between the observer and the Sun
, a unit conversion factor, is the constant 1 AU, the average distance between the Earth and the Sun
Approximations for phase integral
The value of depends on the properties of the reflecting surface, in particular on its roughness. In practice, different approximations are used based on the known or assumed properties of the surface. The surfaces of terrestrial planets are generally more difficult to model than those of gaseous planets, the latter of which have smoother visible surfaces.
Planets as diffuse spheres
Planetary bodies can be approximated reasonably well as ideal diffuse reflecting spheres. Let be the phase angle in degrees, then
A full-phase diffuse sphere reflects two-thirds as much light as a diffuse flat disk of the same diameter. A quarter phase () has as much light as full phase ().
By contrast, a diffuse disk reflector model is simply , which isn't realistic, but it does represent the opposition surge for rough surfaces that reflect more uniform light back at low phase angles.
The definition of the geometric albedo , a measure for the reflectivity of planetary surfaces, is based on the diffuse disk reflector model. The absolute magnitude , diameter (in kilometers) and geometric albedo of a body are related by
or equivalently,
Example: The Moon's absolute magnitude can be calculated from its diameter and geometric albedo : | Absolute magnitude | Wikipedia | 509 | 1963 | https://en.wikipedia.org/wiki/Absolute%20magnitude | Physical sciences | Basics | Astronomy |
We have ,
At quarter phase, (according to the diffuse reflector model), this yields an apparent magnitude of The actual value is somewhat lower than that, This is not a good approximation, because the phase curve of the Moon is too complicated for the diffuse reflector model. A more accurate formula is given in the following section.
More advanced models
Because Solar System bodies are never perfect diffuse reflectors, astronomers use different models to predict apparent magnitudes based on known or assumed properties of the body. For planets, approximations for the correction term in the formula for have been derived empirically, to match observations at different phase angles. The approximations recommended by the Astronomical Almanac are (with in degrees):
Here is the effective inclination of Saturn's rings (their tilt relative to the observer), which as seen from Earth varies between 0° and 27° over the course of one Saturn orbit, and is a small correction term depending on Uranus' sub-Earth and sub-solar latitudes. is the Common Era year. Neptune's absolute magnitude is changing slowly due to seasonal effects as the planet moves along its 165-year orbit around the Sun, and the approximation above is only valid after the year 2000. For some circumstances, like for Venus, no observations are available, and the phase curve is unknown in those cases. The formula for the Moon is only applicable to the near side of the Moon, the portion that is visible from the Earth.
Example 1: On 1 January 2019, Venus was from the Sun, and from Earth, at a phase angle of (near quarter phase). Under full-phase conditions, Venus would have been visible at Accounting for the high phase angle, the correction term above yields an actual apparent magnitude of This is close to the value of predicted by the Jet Propulsion Laboratory.
Example 2: At first quarter phase, the approximation for the Moon gives With that, the apparent magnitude of the Moon is close to the expected value of about . At last quarter, the Moon is about 0.06 mag fainter than at first quarter, because that part of its surface has a lower albedo.
Earth's albedo varies by a factor of 6, from 0.12 in the cloud-free case to 0.76 in the case of altostratus cloud. The absolute magnitude in the table corresponds to an albedo of 0.434. Due to the variability of the weather, Earth's apparent magnitude cannot be predicted as accurately as that of most other planets.
Asteroids | Absolute magnitude | Wikipedia | 508 | 1963 | https://en.wikipedia.org/wiki/Absolute%20magnitude | Physical sciences | Basics | Astronomy |
If an object has an atmosphere, it reflects light more or less isotropically in all directions, and its brightness can be modelled as a diffuse reflector. Bodies with no atmosphere, like asteroids or moons, tend to reflect light more strongly to the direction of the incident light, and their brightness increases rapidly as the phase angle approaches . This rapid brightening near opposition is called the opposition effect. Its strength depends on the physical properties of the body's surface, and hence it differs from asteroid to asteroid.
In 1985, the IAU adopted the semi-empirical -system, based on two parameters and called absolute magnitude and slope, to model the opposition effect for the ephemerides published by the Minor Planet Center.
where
the phase integral is and
for or , , , and .
This relation is valid for phase angles , and works best when .
The slope parameter relates to the surge in brightness, typically , when the object is near opposition. It is known accurately only for a small number of asteroids, hence for most asteroids a value of is assumed. In rare cases, can be negative. An example is 101955 Bennu, with .
In 2012, the -system was officially replaced by an improved system with three parameters , and , which produces more satisfactory results if the opposition effect is very small or restricted to very small phase angles. However, as of 2022, this -system has not been adopted by either the Minor Planet Center nor Jet Propulsion Laboratory.
The apparent magnitude of asteroids varies as they rotate, on time scales of seconds to weeks depending on their rotation period, by up to or more. In addition, their absolute magnitude can vary with the viewing direction, depending on their axial tilt. In many cases, neither the rotation period nor the axial tilt are known, limiting the predictability. The models presented here do not capture those effects.
Cometary magnitudes
The brightness of comets is given separately as total magnitude (, the brightness integrated over the entire visible extend of the coma) and nuclear magnitude (, the brightness of the core region alone). Both are different scales than the magnitude scale used for planets and asteroids, and can not be used for a size comparison with an asteroid's absolute magnitude .
The activity of comets varies with their distance from the Sun. Their brightness can be approximated as | Absolute magnitude | Wikipedia | 465 | 1963 | https://en.wikipedia.org/wiki/Absolute%20magnitude | Physical sciences | Basics | Astronomy |
where are the total and nuclear apparent magnitudes of the comet, respectively, are its "absolute" total and nuclear magnitudes, and are the body-sun and body-observer distances, is the Astronomical Unit, and are the slope parameters characterising the comet's activity. For , this reduces to the formula for a purely reflecting body (showing no cometary activity).
For example, the lightcurve of comet C/2011 L4 (PANSTARRS) can be approximated by On the day of its perihelion passage, 10 March 2013, comet PANSTARRS was from the Sun and from Earth. The total apparent magnitude is predicted to have been at that time. The Minor Planet Center gives a value close to that, .
The absolute magnitude of any given comet can vary dramatically. It can change as the comet becomes more or less active over time or if it undergoes an outburst. This makes it difficult to use the absolute magnitude for a size estimate. When comet 289P/Blanpain was discovered in 1819, its absolute magnitude was estimated as . It was subsequently lost and was only rediscovered in 2003. At that time, its absolute magnitude had decreased to , and it was realised that the 1819 apparition coincided with an outburst. 289P/Blanpain reached naked eye brightness (5–8 mag) in 1819, even though it is the comet with the smallest nucleus that has ever been physically characterised, and usually doesn't become brighter than 18 mag.
For some comets that have been observed at heliocentric distances large enough to distinguish between light reflected from the coma, and light from the nucleus itself, an absolute magnitude analogous to that used for asteroids has been calculated, allowing to estimate the sizes of their nuclei.
Meteors
For a meteor, the standard distance for measurement of magnitudes is at an altitude of at the observer's zenith. | Absolute magnitude | Wikipedia | 382 | 1963 | https://en.wikipedia.org/wiki/Absolute%20magnitude | Physical sciences | Basics | Astronomy |
Alpha Centauri (, α Cen, or Alpha Cen) is a triple star system in the southern constellation of Centaurus. It consists of three stars: Rigil Kentaurus (), Toliman (), and Proxima Centauri (). Proxima Centauri is the closest star to the Sun at 4.2465 light-years (1.3020 pc).
and B are Sun-like stars (class G and K, respectively) that together form the binary star system . To the naked eye, these two main components appear to be a single star with an apparent magnitude of −0.27. It is the brightest star in the constellation and the third-brightest in the night sky, outshone by only Sirius and Canopus.
(Rigil Kentaurus) has 1.1 times the mass and 1.5 times the luminosity of the Sun, while (Toliman) is smaller and cooler, at 0.9 solar masses and less than 0.5 solar luminosities. The pair orbit around a common centre with an orbital period of 79 years. Their elliptical orbit is eccentric, so that the distance between A and B varies from 35.6 astronomical units (AU), or about the distance between Pluto and the Sun, to or about the distance between Saturn and the Sun. One astronomical unit is the distance from Earth to the Sun, 150 million kilometers.
Proxima Centauri, or , is a small faint red dwarf (class M). Though not visible to the naked eye, Proxima Centauri is the closest star to the Sun at a distance of , slightly closer than . Currently, the distance between Proxima Centauri and is about , equivalent to about 430 times the radius of Neptune's orbit.
Proxima Centauri has one confirmed planet: Proxima b, an Earth-sized planet in the habitable zone (though it is unlikely to be habitable), one candidate planet, Proxima d, sub-Earth which orbits very closely to the star, and the controversial Proxima c, a mini-Neptune astronomical units away. may have a Neptune-sized planet in the habitable zone, though it is not yet known with certainty to be planetary in nature and could be an artifact of the discovery mechanism. has no known planets: Planet , purportedly discovered in 2012, was later disproven, and no other planet has yet been confirmed. | Alpha Centauri | Wikipedia | 509 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
Etymology and nomenclature
α Centauri (Latinised to Alpha Centauri) is the system's designation given by J. Bayer in 1603. It belongs to the constellation Centaurus, named after the half human, half horse creature in Greek mythology. Heracles accidentally wounded the centaur and placed him in the sky after his death. Alpha Centauri marks the right front hoof of the Centaur. The common name Rigil Kentaurus is a Latinisation of the Arabic translation Rijl al-Qinṭūrus, meaning "the Foot of the Centaur". Qinṭūrus is the Arabic transliteration of the Greek (Kentaurus). The name is frequently abbreviated to Rigil Kent () or even Rigil, though the latter name is better known for Rigel ( Orionis).
An alternative name found in European sources, Toliman, is an approximation of the Arabic aẓ-Ẓalīmān (in older transcription, aṭ-Ṭhalīmān), meaning 'the (two male) Ostriches', an appellation Zakariya al-Qazwini had applied to the pair of stars Lambda and Mu Sagittarii; it was often not clear on old star maps which name was intended to go with which star (or stars), and the referents changed over time. The name Toliman originates with Jacobus Golius' 1669 edition of Al-Farghani's Compendium. Tolimân is Golius' Latinisation of the Arabic name "the ostriches", the name of an asterism of which Alpha Centauri formed the main star.
was discovered in 1915 by Robert T. A. Innes, who suggested that it be named Proxima Centaurus, . The name Proxima Centauri later became more widely used and is now listed by the International Astronomical Union (IAU) as the approved proper name; it is frequently abbreviated to Proxima.
In 2016, the Working Group on Star Names of the IAU, having decided to attribute proper names to individual component stars rather than to multiple systems, approved the name Rigil Kentaurus () as being restricted to and the name Proxima Centauri () for On 10 August 2018, the IAU approved the name Toliman () for | Alpha Centauri | Wikipedia | 475 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
Other names
During the 19th century, the northern amateur popularist E.H. Burritt used the now-obscure name Bungula (). Its origin is not known, but it may have been coined from the Greek letter beta () and Latin 'hoof', originally for Beta Centauri (the other hoof).
In Chinese astronomy, Nán Mén, meaning Southern Gate, refers to an asterism consisting of Alpha Centauri and Epsilon Centauri. Consequently, the Chinese name for Alpha Centauri itself is Nán Mén Èr, the Second Star of the Southern Gate.
To the Indigenous Boorong people of northwestern Victoria in Australia, Alpha Centauri and Beta Centauri are Bermbermgle, two brothers noted for their courage and destructiveness, who speared and killed Tchingal "The Emu" (the Coalsack Nebula). The form in Wotjobaluk is Bram-bram-bult.
Observation
To the naked eye, appears to be a single star, the brightest in the southern constellation of Centaurus. Their apparent angular separation varies over about 80 years between 2 and 22 arcseconds (the naked eye has a resolution of 60 arcsec), but through much of the orbit, both are easily resolved in binoculars or small telescopes. At −0.27 apparent magnitude (combined for A and B magnitudes ), Alpha Centauri is a first-magnitude star and is fainter only than Sirius and Canopus. It is the outer star of The Pointers or The Southern Pointers, so called because the line through Beta Centauri (Hadar/Agena), some 4.5° west, points to the constellation Crux—the Southern Cross. The Pointers easily distinguish the true Southern Cross from the fainter asterism known as the False Cross.
South of about 29° South latitude, is circumpolar and never sets below the horizon. North of about 29° N latitude, Alpha Centauri never rises. Alpha Centauri lies close to the southern horizon when viewed from the 29° North latitude to the equator (close to Hermosillo and Chihuahua City in Mexico; Galveston, Texas; Ocala, Florida; and Lanzarote, the Canary Islands of Spain), but only for a short time around its culmination. The star culminates each year at local midnight on 24 April and at local 9 p.m. on 8 June. | Alpha Centauri | Wikipedia | 503 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
As seen from Earth, Proxima Centauri is 2.2° southwest from this distance is about four times the angular diameter of the Moon. Proxima Centauri appears as a deep-red star of a typical apparent magnitude of 11.1 in a sparsely populated star field, requiring moderately sized telescopes to be seen. Listed as V645 Cen in the General Catalogue of Variable Stars, version 4.2, this UV Ceti star or "flare star" can unexpectedly brighten rapidly by as much as 0.6 magnitude at visual wavelengths, then fade after only a few minutes. Some amateur and professional astronomers regularly monitor for outbursts using either optical or radio telescopes. In August 2015, the largest recorded flares of the star occurred, with the star becoming 8.3 times brighter than normal on 13 August, in the B band (blue light region).
Alpha Centauri may be inside the G-cloud of the Local Bubble, and its nearest known system is the binary brown dwarf system Luhman 16, at from it.
Observational history
Alpha Centauri is listed in the 2nd century the star catalog appended to Ptolemy's Almagest. He gave its ecliptic coordinates, but texts differ as to whether the ecliptic latitude reads or . (Presently the ecliptic latitude is , but it has decreased by a fraction of a degree since Ptolemy's time due to proper motion.) In Ptolemy's time, Alpha Centauri was visible from Alexandria, Egypt, at but, due to precession, its declination is now , and it can no longer be seen at that latitude. English explorer Robert Hues brought Alpha Centauri to the attention of European observers in his 1592 work Tractatus de Globis, along with Canopus and Achernar, noting:
The binary nature of Alpha Centauri AB was recognized in December 1689 by Jean Richaud, while observing a passing comet from his station in Puducherry. Alpha Centauri was only the third binary star to be discovered, preceded by Mizar AB and Acrux. | Alpha Centauri | Wikipedia | 431 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
The large proper motion of Alpha Centauri AB was discovered by Manuel John Johnson, observing from Saint Helena, who informed Thomas Henderson at the Royal Observatory, Cape of Good Hope of it. The parallax of Alpha Centauri was subsequently determined by Henderson from many exacting positional observations of the AB system between April 1832 and May 1833. He withheld his results, however, because he suspected they were too large to be true, but eventually published them in 1839 after Bessel released his own accurately determined parallax for in 1838. For this reason, Alpha Centauri is sometimes considered as the second star to have its distance measured because Henderson's work was not fully acknowledged at first. (The distance of Alpha Centauri from the Earth is now reckoned at 4.396 light-years or .)
Later, John Herschel made the first micrometrical observations in 1834. Since the early 20th century, measures have been made with photographic plates.
By 1926, William Stephen Finsen calculated the approximate orbit elements close to those now accepted for this system. All future positions are now sufficiently accurate for visual observers to determine the relative places of the stars from a binary star ephemeris. Others, like D. Pourbaix (2002), have regularly refined the precision of new published orbital elements.
Robert T. A. Innes discovered Proxima Centauri in 1915 by blinking photographic plates taken at different times during a proper motion survey. These showed large proper motion and parallax similar in both size and direction to those of which suggested that Proxima Centauri is part of the system and slightly closer to Earth than . As such, Innes concluded that Proxima Centauri was the closest star to Earth yet discovered.
Kinematics
All components of display significant proper motion against the background sky. Over centuries, this causes their apparent positions to slowly change. Proper motion was unknown to ancient astronomers. Most assumed that the stars were permanently fixed on the celestial sphere, as stated in the works of the philosopher Aristotle. In 1718, Edmond Halley found that some stars had significantly moved from their ancient astrometric positions. | Alpha Centauri | Wikipedia | 437 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
In the 1830s, Thomas Henderson discovered the true distance to by analysing his many astrometric mural circle observations. He then realised this system also likely had a high proper motion. In this case, the apparent stellar motion was found using Nicolas Louis de Lacaille's astrometric observations of 1751–1752, by the observed differences between the two measured positions in different epochs.
Calculated proper motion of the centre of mass for is about 3620 mas/y (milliarcseconds per year) toward the west and 694 mas/y toward the north, giving an overall motion of 3686 mas/y in a direction 11° north of west. The motion of the centre of mass is about 6.1 arcmin each century, or 1.02° each millennium. The speed in the western direction is and in the northerly direction . Using spectroscopy the mean radial velocity has been determined to be around towards the Solar System. This gives a speed with respect to the Sun of , very close to the peak in the distribution of speeds of nearby stars.
Since is almost exactly in the plane of the Milky Way as viewed from Earth, many stars appear behind it. In early May 2028, will pass between the Earth and a distant red star, when there is a 45% probability that an Einstein ring will be observed. Other conjunctions will also occur in the coming decades, allowing accurate measurement of proper motions and possibly giving information on planets.
Predicted future changes | Alpha Centauri | Wikipedia | 297 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
Based on the system's common proper motion and radial velocities, will continue to change its position in the sky significantly and will gradually brighten. For example, in about 6,200 CE, α Centauri's true motion will cause an extremely rare first-magnitude stellar conjunction with Beta Centauri, forming a brilliant optical double star in the southern sky. It will then pass just north of the Southern Cross or Crux, before moving northwest and up towards the present celestial equator and away from the galactic plane. By about 26,700 CE, in the present-day constellation of Hydra, will reach perihelion at away, though later calculations suggest that this will occur in 27,000 AD. At its nearest approach, α Centauri will attain a maximum apparent magnitude of −0.86, comparable to present-day magnitude of Canopus, but it will still not surpass that of Sirius, which will brighten incrementally over the next 60,000 years, and will continue to be the brightest star as seen from Earth (other than the Sun) for the next 210,000 years.
Stellar system
Alpha Centauri is a triple star system, with its two main stars, A and B, together comprising a binary component. The AB designation, or older A×B, denotes the mass centre of a main binary system relative to companion star(s) in a multiple star system. AB-C refers to the component of Proxima Centauri in relation to the central binary, being the distance between the centre of mass and the outlying companion. Because the distance between Proxima (C) and either of Alpha Centauri A or B is similar, the AB binary system is sometimes treated as a single gravitational object.
Orbital properties
The A and B components of Alpha Centauri have an orbital period of 79.762 years. Their orbit is moderately eccentric, as it has an eccentricity of almost 0.52; their closest approach or periastron is , or about the distance between the Sun and Saturn; and their furthest separation or apastron is , about the distance between the Sun and Pluto. The most recent periastron was in August 1955 and the next will occur in May 2035; the most recent apastron was in May 1995 and will next occur in 2075. | Alpha Centauri | Wikipedia | 479 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
Viewed from Earth, the apparent orbit of A and B means that their separation and position angle (PA) are in continuous change throughout their projected orbit. Observed stellar positions in 2019 are separated by 4.92 arcsec through the PA of 337.1°, increasing to 5.49 arcsec through 345.3° in 2020. The closest recent approach was in February 2016, at 4.0 arcsec through the PA of 300°. The observed maximum separation of these stars is about 22 arcsec, while the minimum distance is 1.7 arcsec. The widest separation occurred during February 1976, and the next will be in January 2056.
Alpha Centauri C is about from Alpha Centauri AB, equivalent to about 5% of the distance between Alpha Centauri AB and the Sun. Until 2017, measurements of its small speed and its trajectory were of too little accuracy and duration in years to determine whether it is bound to Alpha Centauri AB or unrelated.
Radial velocity measurements made in 2017 were precise enough to show that Proxima Centauri and Alpha Centauri AB are gravitationally bound. The orbital period of Proxima Centauri is approximately years, with an eccentricity of 0.5, much more eccentric than Mercury's. Proxima Centauri comes within of AB at periastron, and its apastron occurs at .
Physical properties
Asteroseismic studies, chromospheric activity, and stellar rotation (gyrochronology) are all consistent with the Alpha Centauri system being similar in age to, or slightly older than, the Sun. Asteroseismic analyses that incorporate tight observational constraints on the stellar parameters for the Alpha Centauri stars have yielded age estimates of Gyr, Gyr, 6.4 Gyr, and Gyr. Age estimates for the stars based on chromospheric activity (Calcium H & K emission) yield whereas gyrochronology yields Gyr. Stellar evolution theory implies both stars are slightly older than the Sun at 5 to 6 billion years, as derived by their mass and spectral characteristics.
From the orbital elements, the total mass of Alpha Centauri AB is about
– or twice that of the Sun. The average individual stellar masses are about and , respectively, though slightly different masses have also been quoted in recent years, such as and , totaling . Alpha Centauri A and B have absolute magnitudes of +4.38 and +5.71, respectively. | Alpha Centauri | Wikipedia | 512 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
Alpha Centauri AB System
Alpha Centauri A
Alpha Centauri A, also known as Rigil Kentaurus, is the principal member, or primary, of the binary system. It is a solar-like main-sequence star with a similar yellowish colour, whose stellar classification is spectral type G2-V; it is about 10% more massive than the Sun, with a radius about 22% larger. When considered among the individual brightest stars in the night sky, it is the fourth-brightest at an apparent magnitude of +0.01, being slightly fainter than Arcturus at an apparent magnitude of −0.05.
The type of magnetic activity on Alpha Centauri A is comparable to that of the Sun, showing coronal variability due to star spots, as modulated by the rotation of the star. However, since 2005 the activity level has fallen into a deep minimum that might be similar to the Sun's historical Maunder Minimum. Alternatively, it may have a very long stellar activity cycle and is slowly recovering from a minimum phase.
Alpha Centauri B
Alpha Centauri B, also known as Toliman, is the secondary star of the binary system. It is a main-sequence star of spectral type K1-V, making it more an orange colour than Alpha Centauri A; it has around 90% of the mass of the Sun and a 14% smaller diameter. Although it has a lower luminosity than A, Alpha Centauri B emits more energy in the X-ray band. Its light curve varies on a short time scale, and there has been at least one observed flare. It is more magnetically active than Alpha Centauri A, showing a cycle of compared to 11 years for the Sun, and has about half the minimum-to-peak variation in coronal luminosity of the Sun. Alpha Centauri B has an apparent magnitude of +1.35, slightly dimmer than Mimosa.
Alpha Centauri C (Proxima Centauri)
Alpha Centauri C, better known as Proxima Centauri, is a small main-sequence red dwarf of spectral class M6-Ve. It has an absolute magnitude of +15.60, over 20,000 times fainter than the Sun. Its mass is calculated to be . It is the closest star to the Sun but is too faint to be visible to the naked eye. | Alpha Centauri | Wikipedia | 498 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
Planetary system
The Alpha Centauri system as a whole has two confirmed planets, both of them around Proxima Centauri. While other planets have been claimed to exist around all of the stars, none of the discoveries have been confirmed.
Planets of Proxima Centauri
Proxima Centauri b is a terrestrial planet discovered in 2016 by astronomers at the European Southern Observatory (ESO). It has an estimated minimum mass of 1.17 (Earth masses) and orbits approximately 0.049 AU from Proxima Centauri, placing it in the star's habitable zone.
The discovery of Proxima Centauri c was formally published in 2020 and could be a super-Earth or mini-Neptune. It has a mass of roughly 7 and orbits about from Proxima Centauri with a period of . In June 2020, a possible direct imaging detection of the planet hinted at the presence of a large ring system. However, a 2022 study disputed the existence of this planet.
A 2020 paper refining Proxima b's mass excludes the presence of extra companions with masses above at periods shorter than 50 days, but the authors detected a radial-velocity curve with a periodicity of 5.15 days, suggesting the presence of a planet with a mass of about . This planet, Proxima Centauri d, was detected in 2022.
Planets of Alpha Centauri A
In 2021, a candidate planet named Candidate 1 (or C1) was detected around Alpha Centauri A, thought to orbit at approximately with a period of about one year, and to have a mass between that of Neptune and one-half that of Saturn, though it may be a dust disk or an artifact. The possibility of C1 being a background star has been ruled out. If this candidate is confirmed, the temporary name C1 will most likely be replaced with the scientific designation Alpha Centauri Ab in accordance with current naming conventions. | Alpha Centauri | Wikipedia | 398 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
GO Cycle 1 observations are planned for the James Webb Space Telescope (JWST) to search for planets around Alpha Centauri A, as well as observations of Epsilon Muscae. The coronographic observations, which occurred on July 26 and 27, 2023, were failures, though there are follow-up observations in March 2024. Pre-launch estimates predicted that JWST will be able to find planets with a radius of 5 at . Multiple observations every 3–6 months could push the limit down to 3 . Post-launch estimates based on observations of HIP 65426 b find that JWST will be able to find planets even closer to Alpha Centauri A and could find a 5 planet at . Candidate 1 has an estimated radius between and orbits at . It is therefore likely within the reach of JWST observations.
Planets of Alpha Centauri B
The first claim of a planet around Alpha Centauri B was that of Alpha Centauri Bb in 2012, which was proposed to be an Earth-mass planet in a 3.2-day orbit. This was refuted in 2015 when the apparent planet was shown to be an artifact of the way the radial velocity data was processed.
A search for transits of planet Bb was conducted with the Hubble Space Telescope from 2013 to 2014. This search detected one potential transit-like event, which could be associated with a different planet with a radius around . This planet would most likely orbit Alpha Centauri B with an orbital period of 20.4 days or less, with only a 5% chance of it having a longer orbit. The median of the likely orbits is 12.4 days. Its orbit would likely have an eccentricity of 0.24 or less. It could have lakes of molten lava and would be far too close to Alpha Centauri B to harbour life. If confirmed, this planet might be called . However, the name has not been used in the literature, as it is not a claimed discovery. | Alpha Centauri | Wikipedia | 405 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
Hypothetical planets
Additional planets may exist in the Alpha Centauri system, either orbiting Alpha Centauri A or Alpha Centauri B individually, or in large orbits around Alpha Centauri AB. Because both stars are fairly similar to the Sun (for example, in age and metallicity), astronomers have been especially interested in making detailed searches for planets in the Alpha Centauri system. Several established planet-hunting teams have used various radial velocity or star transit methods in their searches around these two bright stars. All the observational studies have so far failed to find evidence for brown dwarfs or gas giants.
In 2009, computer simulations showed that a planet might have been able to form near the inner edge of Alpha Centauri B's habitable zone, which extends from from the star. Certain special assumptions, such as considering that the Alpha Centauri pair may have initially formed with a wider separation and later moved closer to each other (as might be possible if they formed in a dense star cluster), would permit an accretion-friendly environment farther from the star. Bodies around Alpha Centauri A would be able to orbit at slightly farther distances due to its stronger gravity. In addition, the lack of any brown dwarfs or gas giants in close orbits around Alpha Centauri make the likelihood of terrestrial planets greater than otherwise. A theoretical study indicates that a radial velocity analysis might detect a hypothetical planet of in Alpha Centauri B's habitable zone.
Radial velocity measurements of Alpha Centauri B made with the High Accuracy Radial Velocity Planet Searcher spectrograph were sufficiently sensitive to detect a planet within the habitable zone of the star (i.e. with an orbital period P = 200 days), but no planets were detected.
Current estimates place the probability of finding an Earth-like planet around Alpha Centauri at roughly 75%. The observational thresholds for planet detection in the habitable zones by the radial velocity method are currently (2017) estimated to be about for Alpha Centauri A, for Alpha Centauri B, and for Proxima Centauri. | Alpha Centauri | Wikipedia | 427 | 1979 | https://en.wikipedia.org/wiki/Alpha%20Centauri | Physical sciences | Notable stars | null |
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