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Conceptual means
Invention is often a creative process. An open and curious mind allows an inventor to see beyond what is known. Seeing a new possibility, connection or relationship can spark an invention. Inventive thinking frequently involves combining concepts or elements from different realms that would not normally be put together. Sometimes inventors disregard the boundaries between distinctly separate territories or fields. Several concepts may be considered when thinking about invention.
Play
Play may lead to invention. Childhood curiosity, experimentation, and imagination can develop one's play instinct. Inventors feel the need to play with things that interest them, and to explore, and this internal drive brings about novel creations.
Sometimes inventions and ideas may seem to arise spontaneously while daydreaming, especially when the mind is free from its usual concerns. For example, both J. K. Rowling (the creator of Harry Potter) and Frank Hornby (the inventor of Meccano) first had their ideas while on train journeys.
In contrast, the successful aerospace engineer Max Munk advocated "aimful thinking".
Re-envisioning
To invent is to see anew. Inventors often envision a new idea, seeing it in their mind's eye. New ideas can arise when the conscious mind turns away from the subject or problem when the inventor's focus is on something else, or while relaxing or sleeping. A novel idea may come in a flash—a Eureka! moment. For example, after years of working to figure out the general theory of relativity, the solution came to Einstein suddenly in a dream "like a giant die making an indelible impress, a huge map of the universe outlined itself in one clear vision". Inventions can also be accidental, such as in the case of polytetrafluoroethylene (Teflon).
Insight
Insight can also be a vital element of invention. Such inventive insights may begin with questions, doubt or a hunch. It may begin by recognizing that something unusual or accidental may be useful or that it could open a new avenue for exploration. For example, the odd metallic color of plastic made by accidentally adding a thousand times too much catalyst led scientists to explore its metal-like properties, inventing electrically conductive plastic and light emitting plastic—an invention that won the Nobel Prize in 2000 and has led to innovative lighting, display screens, wallpaper and much more (see conductive polymer, and organic light-emitting diode or OLED).
Exploration | Invention | Wikipedia | 500 | 44312 | https://en.wikipedia.org/wiki/Invention | Technology | Technology: General | null |
Invention is often an exploratory process with an uncertain or unknown outcome. There are failures as well as successes. Inspiration can start the process, but no matter how complete the initial idea, inventions typically must be developed.
Improvement
Inventors may, for example, try to improve something by making it more effective, healthier, faster, more efficient, easier to use, serve more purposes, longer lasting, cheaper, more ecologically friendly, or aesthetically different, lighter weight, more ergonomic, structurally different, with new light or color properties, etc.
Implementation
In economic theory, inventions are one of the chief examples of "positive externalities", a beneficial side effect that falls on those outside a transaction or activity. One of the central concepts of economics is that externalities should be internalized—unless some of the benefits of this positive externality can be captured by the parties, the parties are under-rewarded for their inventions, and systematic under-rewarding leads to under-investment in activities that lead to inventions. The patent system captures those positive externalities for the inventor or other patent owner so that the economy as a whole invests an optimum amount of resources in the invention process.
Comparison with innovation
In contrast to invention, innovation is the implementation of a creative idea that specifically leads to greater value or usefulness. That is, while an invention may be useless or have no value yet still be an invention, an innovation must have some sort of value, typically economic.
As defined by patent law
The term invention is also an important legal concept and central to patent law systems worldwide. As is often the case for legal concepts, its legal meaning is slightly different from common usage of the word. Additionally, the legal concept of invention is quite different in American and European patent law. | Invention | Wikipedia | 361 | 44312 | https://en.wikipedia.org/wiki/Invention | Technology | Technology: General | null |
In Europe, the first test a patent application must pass is, "Is this an invention?" If it is, subsequent questions are whether it is new and sufficiently inventive. The implication—counter-intuitively—is that a legal invention is not inherently novel. Whether a patent application relates to an invention is governed by Article 52 of the European Patent Convention, that excludes, e.g., discoveries as such and software as such. The EPO Boards of Appeal decided that the technical character of an application is decisive for it to represent an invention, following an age-old Italian and German tradition. British courts do not agree with this interpretation. Following a 1959 Australian decision ("NRDC"), they believe that it is not possible to grasp the invention concept in a single rule. A British court once stated that the technical character test implies a "restatement of the problem in more imprecise terminology."
In the United States, all patent applications are considered inventions. The statute explicitly says that the American invention concept includes discoveries (35 USC § 100(a)), contrary to the European invention concept. The European invention concept corresponds to the American "patentable subject matter" concept: the first test a patent application is submitted to. While the statute (35 USC § 101) virtually poses no limits to patenting whatsoever, courts have decided in binding precedents that abstract ideas, natural phenomena and laws of nature are not patentable. Various attempts have been made to substantiate the "abstract idea" test, which suffers from abstractness itself, but none have succeeded. The last attempt so far was the "machine or transformation" test, but the U.S. Supreme Court decided in 2010 that it is merely an indication at best.
In India, invention means a new product or process that involves an inventive step, and capable of being made or used in an industry. Whereas, "new invention" means any invention that has not been anticipated in any prior art or used in the country or anywhere in the world.
In the arts
Invention has a long and important history in the arts. Inventive thinking has always played a vital role in the creative process. While some inventions in the arts are patentable, others are not because they cannot fulfill the strict requirements governments have established for granting them. (see patent). | Invention | Wikipedia | 477 | 44312 | https://en.wikipedia.org/wiki/Invention | Technology | Technology: General | null |
Some inventions in art include the:
Collage and construction invented by Picasso
Readymade art invented by Marcel Duchamp
mobile invented by Alexander Calder
Combine invented by Robert Rauschenberg
Shaped painting invented by Frank Stella
Motion picture, the invention of which is attributed to Eadweard Muybridge
Video art invented by Nam June Paik
Likewise, Jackson Pollock invented an entirely new form of painting and a new kind of abstraction by dripping, pouring, splashing and splattering paint onto un-stretched canvas lying on the floor.
Inventive tools of the artist's trade also produced advances in creativity. Impressionist painting became possible because of newly invented collapsible, resealable metal paint tubes that facilitated spontaneous painting outdoors. Inventions originally created in the form of artwork can also develop other uses, e.g. Alexander Calder's mobile, which is now commonly used over babies' cribs. Funds generated from patents on inventions in art, design and architecture can support the realization of the invention or other creative work. Frédéric Auguste Bartholdi's 1879 design patent on the Statue of Liberty helped fund the famous statue because it covered small replicas, including those sold as souvenirs.
The timeline for invention in the arts lists the most notable artistic inventors.
Gender gap in inventions
Historically, women in many regions have been unrecognised for their inventive contributions (except Russia and France), despite being the sole inventor or co-inventor in inventions, including highly notable inventions. Notable examples include Margaret Knight who faced significant challenges in receiving credit for her inventions; Elizabeth Magie who was not credited for her invention of the game of Monopoly; and among other such examples, Chien-Shiung Wu whose male colleagues alone were awarded the Nobel Prize for their joint contributions to physics. Societal prejudice, institutional, educational and often legal patent barriers have both played a role in the gender invention gap. For example, although there could be found female patenters in US patent Office who also are likely to be helpful in their experience, still a patent applications made to the US Patent Office for inventions are less likely to succeed where the applicant have a "feminine" name, and additionally women could lose their independent legal patent rights to their husbands once married. | Invention | Wikipedia | 456 | 44312 | https://en.wikipedia.org/wiki/Invention | Technology | Technology: General | null |
Clovers, also called trefoils, are plants of the genus Trifolium (), consisting of about 300 species of flowering plants in the legume family Fabaceae originating in Europe. The genus has a cosmopolitan distribution with the highest diversity in the temperate Northern Hemisphere, but many species also occur in South America and Africa, including at high altitudes on mountains in the tropics.
They are small annual, biennial, or short-lived perennial herbaceous plants, typically growing up to tall. The leaves are trifoliate (rarely, they have less or more than three leaflets; the more leaflets the leaf has, the rarer it is; see four-leaf clover), with stipules adnate to the leaf-stalk, and heads or dense spikes of small red, purple, white, or yellow flowers; the small, few-seeded pods are enclosed in the calyx. Other closely related genera often called clovers include Melilotus (sweet clover) and Medicago (alfalfa or Calvary clover).
As legumes, clovers fix nitrogen using symbiotic bacteria in their root nodules, and are used as an alternative or supplement to synthetic nitrogen fertilizers. They are also valuable food source for grazing livestock and bees. The domestication of clover caused substantial increases in agricultural productivity.
Cultivation history
Clover was first domesticated in Spain in around the year 1000. During European urbanization, crop rotations involving clover became essential for replacing the fixed nitrogen exported to cities as food. Increased soil nitrogen levels from the spreading use of clover were one of the main reasons why European agricultural production in 1880 was about 275% of the production in 1750. Fields of clover, used as forage and newly-invented silage, became an important part of the rural landscape; adding clover made livestock feed more nutritious. Honey production also rose drastically, and clover remained the main nectar source for bees until the mid-twentieth century. Clover was carried around the world as a crop by European colonists, and some clover species became invasive in some areas. | Clover | Wikipedia | 422 | 44344 | https://en.wikipedia.org/wiki/Clover | Biology and health sciences | Fabales | Plants |
Imports of guano and the development of the Haber-Bosch process in the 20th century substantially displaced clover as a crop, with negative effects on pollinators, but in the 1990s and 2010s, the cost of industrially-fixed nitrogen rose substantially, approximately doubling, and reviving interest in forage mixes that include clover. As the fixation process is energy-intensive, prices are closely tied to energy prices. The 21st century also saw interest in clover as a countermeasure to fight the global pollinator decline.
Cultivation
Several species of clover are extensively cultivated as fodder plants. The most widely cultivated clovers are white clover, Trifolium repens, and red clover, Trifolium pratense. Clover, either sown alone or in mixture with ryegrass, has for a long time formed a staple crop for silaging, for several reasons: it grows freely, shooting up again after repeated mowings; it produces an abundant crop; it is palatable to and nutritious for livestock; it fixes nitrogen using symbiotic bacteria in its root nodules, reducing the need for synthetic fertilizers; it grows in a great range of soils and climates; and it is appropriate for either pasturage or green composting.
In many areas, particularly on acidic soil, clover is short-lived because of a combination of insect pests, diseases and nutrient balance; this is known as "clover sickness". When crop rotations are managed so that clover does not recur at intervals shorter than eight years, it grows with much of its pristine vigor.
Clovers are most efficiently pollinated by bumblebees, which have declined as a result of agricultural intensification. Honeybees can also pollinate clover, and beekeepers are often in heavy demand from farmers with clover pastures. Farmers reap the benefits of increased reseeding that occurs with increased bee activity, which means that future clover yields remain abundant. Beekeepers benefit from the clover bloom, as clover is one of the main nectar sources for honeybees. | Clover | Wikipedia | 423 | 44344 | https://en.wikipedia.org/wiki/Clover | Biology and health sciences | Fabales | Plants |
Trifolium repens, white or Dutch clover, is a perennial abundant in meadows and good pastures. The flowers are white or pinkish, becoming brown and deflexed as the corolla fades. Trifolium hybridum, alsike or Swedish clover, is a perennial which was introduced early in the 19th century and has now become naturalized in Britain. The flowers are white or rosy, and resemble those of Trifolium repens. Trifolium medium, meadow or zigzag clover, a perennial with straggling flexuous stems and rose-purple flowers, has potential for interbreeding with T. pratense to produce perennial crop plants.
Other species are: Trifolium arvense, hare's-foot trefoil; found in fields and dry pastures, a soft hairy plant with minute white or pale pink flowers and feathery sepals; Trifolium fragiferum, strawberry clover, with globose, rose-purple heads and swollen calyxes; Trifolium campestre, hop trefoil, on dry pastures and roadsides, the heads of pale yellow flowers suggesting miniature hops; and the somewhat similar Trifolium dubium, common in pastures and roadsides, with smaller heads and small yellow flowers turning dark brown.
Uses
Clover is foraged for by wildlife such as bears, game animals, and birds. Clover is edible by humans, although red clover should be avoided by pregnant women. The plant is a traditional Native American food, which is eaten both raw and after drying and smoking the roots. The seeds from the blossoms are used to make bread. It is also possible to make tea from the blossoms.
Symbolism
Shamrock, the traditional Irish symbol, which according to legend was coined by Saint Patrick for the Holy Trinity, is commonly associated with clover, although alternatively sometimes with the various species within the genus Oxalis, which are also trifoliate.
Clovers occasionally have four leaflets, instead of the usual three. These four-leaf clovers, like other rarities, are considered lucky. Clovers can also have five, six, or more leaflets, but these are rarer still. The clover's outer leaf structure varies in physical orientation. | Clover | Wikipedia | 451 | 44344 | https://en.wikipedia.org/wiki/Clover | Biology and health sciences | Fabales | Plants |
The record for most leaflets is 63, set on August 2, 2023, by Yoshiharu Watanabe in Japan. The previous record holder, Shigeo Obara, had discovered an 18-leaf clover in 2002, a 21-leaf clover in 2008 and a 56-leaf clover in 2009, also in Japan.
A common idiom is "to be (or to live) in clover", meaning to live a carefree life of ease, comfort, or prosperity.
A common saying in surgery [regarding the appearance of wound after hemorrhoidectomy] is "If it looks like clover, the trouble is over; if it looks like dahlia, it’s surely a failure."
A cloverleaf interchange is named for the resemblance to the leaflets of a (four-leaf) clover when viewed from the air. | Clover | Wikipedia | 173 | 44344 | https://en.wikipedia.org/wiki/Clover | Biology and health sciences | Fabales | Plants |
Phylogeny
The first extensive classification of Trifolium had been done by Michael Zohary and David Heller, and it was subsequently released in 1984. They divided the genus into eight sections: Lotoidea, Paramesus, Mistyllus, Vesicamridula, Chronosemium, Trifolium, Trichoecephalum, and Involucrarium, with Lotoidea placed most basally. Within this classification system, Trifolium repens falls within section Lotoidea, the largest and least heterogeneous section. Lotoidea contains species from America, Africa, and Eurasia, considered a clade because of their inflorescence shape, floral structure, and legume that protrudes from the calyx. However, these traits are not unique to the section, and are shared with many other species in other sections. Zohary and Heller argued that the presence of these traits in other sections proved the basal position of Lotoidea, because they were ancestral. Aside from considering this section basal, they did not propose relationships between other sections.
Since then, molecular data has both questioned and confirmed the proposed phylogeny from Zohary and Heller. A genus-wide molecular study has since proposed a new classification system, made up of two subgenera, Chronosemium and Trifolium. This recent reclassification further divides subgenus Trifolium into eight sections. The molecular data supports the monophyletic nature of three sections proposed by Zohary and Heller (Tripholium, Paramesus, and Trichoecepalum), but not of Lotoidea (members of this section have since been reclassified into five other sections). Other molecular studies, although smaller, support the need to reorganize Lotoidea.
Species
291 species of Trifolium are accepted: | Clover | Wikipedia | 379 | 44344 | https://en.wikipedia.org/wiki/Clover | Biology and health sciences | Fabales | Plants |
Trifolium absconditum
Trifolium acaule Steud. ex A.Rich.
Trifolium affine C.Presl
Trifolium acutiflorum
Trifolium × adulterinum
Trifolium affine
Trifolium africanum Ser.
Trifolium aintabense Boiss. & Hausskn.
Trifolium albopurpureum Torr. & A. Gray – rancheria clover
Trifolium alexandrinum L. – Egyptian clover, berseem clover
Trifolium alpestre L. – owl-head clover
Trifolium alpinum L. – alpine clover
Trifolium alsadami
Trifolium amabile Kunth
Trifolium ambiguum M. Bieb.
Trifolium amoenum Greene – showy Indian clover
Trifolium amphianthum
Trifolium andersonii A. Gray – Anderson's clover or fiveleaf clover
Trifolium andinum Nutt. – Intermountain clover
Trifolium andricum Lassen
Trifolium angulatum Waldst. & Kit.
Trifolium angustifolium L.
Trifolium ankaratrense
Trifolium apertum Bobrov
Trifolium appendiculatum
Trifolium argutum Banks & Sol.
Trifolium arvense L. – hare's-foot clover
Trifolium attenuatum Greene
Trifolium aureum Pollich – large hop trefoil
Trifolium baccarinii Chiov.
Trifolium badium Schreb.
Trifolium barbigerum Torr. – bearded clover
Trifolium barbulatum
Trifolium barnebyi (Isely) Dorn & Lichvar
Trifolium batmanicum Katzn.
Trifolium beckwithii W.H.Brewer ex S.Watson – Beckwith's clover
Trifolium bejariense Moric.
Trifolium × bertrandii
Trifolium berytheum Boiss. & C.I.Blanche
Trifolium biebersteinii
Trifolium bifidum A.Gray – notchleaf clover
Trifolium bilineatum Fresen.
Trifolium billardierei Spreng.
Trifolium bithynicum
Trifolium bivonae Guss.
Trifolium blancheanum Boiss.
Trifolium bobrovii
Trifolium bocconei Savi
Trifolium boissieri Guss. | Clover | Wikipedia | 512 | 44344 | https://en.wikipedia.org/wiki/Clover | Biology and health sciences | Fabales | Plants |
Trifolium bolanderi A.Gray
Trifolium bordsilovskyi
Trifolium brandegeei S.Watson
Trifolium breweri S. Watson – forest clover
Trifolium brutium Ten.
Trifolium buckwestiorum Isely – Santa Cruz clover
Trifolium bullatum Boiss. & Hausskn.
Trifolium burchellianum Ser.
Trifolium calcaricum J.L.Collins & Wieboldt
Trifolium calocephalum Fresen.
Trifolium campestre Schreb. – hop trefoil
Trifolium canescens Willd.
Trifolium carolinianum Michx.
Trifolium caudatum Boiss.
Trifolium cernuum Brot.
Trifolium cheranganiense J.B.Gillett
Trifolium cherleri L.
Trifolium chilaloense Thulin
Trifolium chilense Hook. & Arn.
Trifolium chlorotrichum Boiss. & Balansa
Trifolium ciliolatum Benth. – foothill clover
Trifolium circumdatum Kunze
Trifolium clusii Godr.
Trifolium clypeatum L.
Trifolium congestum Guss.
Trifolium constantinopolitanum Ser.
Trifolium cryptopodium Steud. ex A. Rich.
Trifolium cyathiferum Lindl. – cup clover
Trifolium dalmaticum Vis.
Trifolium dasyphyllum Torr. & A.Gray
Trifolium dasyurum C.Presl
Trifolium davisii E.Hossain
Trifolium decorum Chiov.
Trifolium dedeckerae
Trifolium depauperatum Desv. – cowbag clover, balloon sack clover, or poverty clover
Trifolium dichotomum Hook. & Arn.
Trifolium dichroanthoides Rech.f.
Trifolium dichroanthum Boiss.
Trifolium diffusum Ehrh.
Trifolium dolopium Heldr. & Hochst. ex Gibelli & Belli
Trifolium douglasii House
Trifolium dubium Sibth. – lesser hop trefoil
Trifolium echinatum M.Bieb.
Trifolium egrissicum
Trifolium elgonense J.B.Gillett
Trifolium elizabethiae | Clover | Wikipedia | 512 | 44344 | https://en.wikipedia.org/wiki/Clover | Biology and health sciences | Fabales | Plants |
Trifolium eriocephalum Nutt. – woollyhead clover
Trifolium eriosphaerum Boiss.
Trifolium erubescens Fenzl
Trifolium euxinum Zohary
Trifolium eximium Stephan ex Ser.
Trifolium farayense
Trifolium fergan-karaeri
Trifolium fontanum
Trifolium fragiferum L. – strawberry clover
Trifolium friscanum (S.L.Welsh) S.L.Welsh
Trifolium fucatum Lindl. – bull clover or sour clover
Trifolium gemellum Pourr. ex Willd.
Trifolium gillettianum Jacq.-Fél.
Trifolium glanduliferum Boiss.
Trifolium globosum L.
Trifolium glomeratum L. – clustered clover or bush clover
Trifolium gordeievii (Kom.) Z.Wei
Trifolium gracilentum Torr. & A.Gray – pinpoint clover
Trifolium grandiflorum Schreb.
Trifolium gymnocarpon Nutt. – hollyleaf clover
Trifolium hatschbachii
Trifolium haussknechtii Boiss.
Trifolium haydenii Porter
Trifolium heldreichianum (Gibelli & Belli) Hausskn.
Trifolium hickeyi
Trifolium hirtum All. – rose clover
Trifolium howellii S.Watson – canyon clover or Howell's clover
Trifolium humile
Trifolium hybridum L. – Alsike clover
Trifolium hydrophilum
Trifolium incarnatum L. – crimson clover
Trifolium infamia-ponertii
Trifolium israeliticum Zohary & Katzn.
Trifolium isthmocarpum Brot.
Trifolium jokerstii Vincent & Rand.Morgan
Trifolium juliani Batt.
Trifolium kentuckiense Chapel & Vincent
Trifolium kingii S.Watson
Trifolium lanceolatum (J.B.Gillett) J.B.Gillett
Trifolium lappaceum L.
Trifolium latifolium (Hook.) Greene
Trifolium latinum Sebast.
Trifolium leibergii A.Nelson & J.F.Macbr. – Leiberg's clover
Trifolium lemmonii S.Watson – Lemmon's clover | Clover | Wikipedia | 512 | 44344 | https://en.wikipedia.org/wiki/Clover | Biology and health sciences | Fabales | Plants |
Trifolium leucanthum M.Bieb.
Trifolium ligusticum Balb. ex Loisel.
Trifolium longidentatum Nábelek
Trifolium longipes Nutt. – longstalk clover
Trifolium lucanicum Gasp.
Trifolium lugardii Bullock
Trifolium lupinaster L.
Trifolium macilentum Greene
Trifolium macraei Hook. & Arn. – Chilean clover, double-head clover, or MacRae's clover
Trifolium macrocephalum (Pursh) Poir. – largehead clover
Trifolium masaiense J.B.Gillett
Trifolium mattirolianum Chiov.
Trifolium mazanderanicum Rech.f.
Trifolium medium L. – zigzag clover
Trifolium meduseum C.I.Blanche ex Boiss.
Trifolium meironense Zohary & Lerner
Trifolium mesogitanum
Trifolium michaelis
Trifolium michelianum Savi
Trifolium micranthum Viv.
Trifolium microcephalum Pursh – smallhead clover
Trifolium microdon Hook. & Arn. – thimble clover
Trifolium miegeanum Maire
Trifolium minutissimum
Trifolium modestum
Trifolium monanthum A.Gray – mountain carpet clover
Trifolium montanum L.
Trifolium multinerve A. Rich.
Trifolium multistriatum W.D.J.Koch
Trifolium mutabile Port.
Trifolium nanum Torr.
Trifolium nerimaniae M.Keskin
Trifolium × neyrautii
Trifolium nigrescens Viv.
Trifolium noricum Wulfen
Trifolium obscurum Savi
Trifolium obtusiflorum Hook. – clammy clover
Trifolium occidentale Coombe
Trifolium ochroleucon Huds. - sulphur clover
Trifolium oliganthum Steud. – fewflower clover
Trifolium olivaceum
Trifolium orbelicum
Trifolium ornithopodioides L.
Trifolium owyheense Gilkey
Trifolium pachycalyx Zohary
Trifolium palaestinum Boiss.
Trifolium pallescens Schreb. | Clover | Wikipedia | 502 | 44344 | https://en.wikipedia.org/wiki/Clover | Biology and health sciences | Fabales | Plants |
Trifolium pallidum Waldst. & Kit.
Trifolium palmeri
Trifolium pamphylicum
Trifolium pannonicum Jacq. – Hungarian clover
Trifolium parnassi Boiss. & Spruner
Trifolium parryi A.Gray
Trifolium patens Schreb.
Trifolium patulum Tausch
Trifolium pauciflorum d'Urv.
Trifolium × permixtum
Trifolium peruvianum Vogel
Trifolium philistaeum Zohary
Trifolium phitosianum N.Böhling, Greuter & Raus
Trifolium phleoides Pourr. ex Willd.
Trifolium physanthum Hook. & Arn.
Trifolium physodes Steven ex M. Bieb.
Trifolium pichisermollii J.B.Gillett
Trifolium pignantii Fauché. & Chaub.
Trifolium pilczii Adamović
Trifolium pilulare Boiss.
Trifolium piorkowskii Rand.Morgan & A.L.Barber
Trifolium plebeium Boiss.
Trifolium plumosum Douglas ex Hook.
Trifolium polymorphum Poir.
Trifolium polyodon Greene
Trifolium polyphyllum C.A.Mey.
Trifolium polystachyum Fresen.
Trifolium praetermissum Greuter, Pleger & Raus.
Trifolium pratense L. – red clover
Trifolium productum
Trifolium prophetarum M. Hossain
Trifolium pseudomedium
Trifolium pseudostriatum Baker f.
Trifolium pulchellum
Trifolium purpureum Loisel.
Trifolium purseglovei J. B. Gillett
Trifolium quartinianum A. Rich.
Trifolium radicosum Boiss. & Hohen.
Trifolium rechingeri
Trifolium reflexum L. – buffalo clover
Trifolium repens L. – shamrock (white clover)
Trifolium resupinatum L. – Persian clover, shaftal
Trifolium retusum L.
Trifolium × retyezaticum
Trifolium rhizomatosum
Trifolium rhombeum
Trifolium riograndense Burkart
Trifolium rollinsii
Trifolium roussaeanum Boiss. | Clover | Wikipedia | 509 | 44344 | https://en.wikipedia.org/wiki/Clover | Biology and health sciences | Fabales | Plants |
Trifolium rubens L.
Trifolium rueppellianum Fresen.
Trifolium salmoneum Mouterde
Trifolium sannineum
Trifolium sarosiense
Trifolium saxatile All.
Trifolium scabrum L.
Trifolium schimperi (Hochst.) A.Rich.
Trifolium schneideri
Trifolium × schwarzii
Trifolium scutatum Boiss.
Trifolium sebastiani Savi
Trifolium semipilosum Fresen.
Trifolium setiferum Boiss.
Trifolium simense Fresen.
Trifolium sintenisii Freyn
Trifolium siskiyouense J.M.Gillett
Trifolium somalense Taub. ex Harms
Trifolium sonorense
Trifolium spadiceum L.
Trifolium spananthum Thulin
Trifolium spumosum L.
Trifolium squamosum (or maritimum) L. – sea clover
Trifolium squarrosum L.
Trifolium stellatum L.
Trifolium steudneri Schweinf.
Trifolium stipulaceum Thunb.
Trifolium stoloniferum Muhl. ex A. Eaton – running buffalo clover
Trifolium stolzii Harms
Trifolium striatum L. – knotted clover
Trifolium strictum L.
Trifolium subterraneum L. – subterranean clover
Trifolium suffocatum L.
Trifolium sylvaticum Gérard
Trifolium tembense Fresen.
Trifolium tenuifolium
Trifolium thalii Vill.
Trifolium thompsonii C.V.Morton – Thompson's clover
Trifolium tomentosum L.
Trifolium × traplii
Trifolium triaristatum Bertero ex Colla
Trifolium trichocalyx A.Heller – Monterey clover
Trifolium trichocephalum M. Bieb.
Trifolium trichopterum Pančić
Trifolium tumens Steven ex M.Bieb.
Trifolium ukingense Harms
Trifolium uniflorum L.
Trifolium usambarense Taub.
Trifolium variegatum Nutt. – whitetip clover
Trifolium vavilovii Eig
Trifolium velebiticum Degen
Trifolium velenovskyi Vandas | Clover | Wikipedia | 511 | 44344 | https://en.wikipedia.org/wiki/Clover | Biology and health sciences | Fabales | Plants |
Trifolium vernum Phil.
Trifolium vesiculosum Savi
Trifolium vestitum D.Heller & Zohary
Trifolium virginicum Small
Trifolium wentzelianum Harms
Trifolium wettsteinii Dörfl. & Hayek
Trifolium wigginsii J. M. Gillett
Trifolium willdenovii Spreng. − tomcat clover
Trifolium wormskioldii Lehm. – cow clover
Trifolium xanthinum | Clover | Wikipedia | 106 | 44344 | https://en.wikipedia.org/wiki/Clover | Biology and health sciences | Fabales | Plants |
The shallot is a cultivar group of the onion. Until 2010, the (French red) shallot was classified as a separate species, Allium ascalonicum. The taxon was synonymized with Allium cepa (the common onion) in 2010, as the difference was too small to justify a separate species.
As part of the onion genus Allium, its close relatives include garlic, scallions, leeks, chives, and the Chinese onion.
Etymology and names
The names scallion and shallot are derived from the Old French eschalotte, by way of eschaloigne, from the Latin Ascalōnia caepa or Ascalonian onion, a Ascalōnia caepa or Ascalonian onion, a namesake of the ancient city of Ascalon.
The term shallot is usually applied to the French red shallot (Allium cepa var. aggregatum, or the A. cepa Aggregatum Group). It is also used for the Persian shallot or musir (A. stipitatum) from the Zagros Mountains in Iran and Iraq, and the French gray shallot (Allium oschaninii) which is also known as griselle or "true shallot"; it grows wild from Central to Southwest Asia. The name shallot is also used for a scallion in New South Wales, Australia and among English-speaking people in Quebec while the term French shallot refers to the plant referred to on this page. In most English-speaking nations, the name is pronounced with the emphasis on the last syllable in common with the French pronunciation, sha-lot, while the emphasis is commonly made on the first syllable, shall-ət, in the United States.
The term eschalot, derived from the French word échalote, can also be used to refer to the shallot.
Description and cultivation
Like garlic, shallots are formed in clusters of offsets with a head composed of multiple cloves. The skin colour of shallots can vary from golden brown to gray to rose red, and their off-white flesh is usually tinged with green or magenta. | Shallot | Wikipedia | 448 | 44346 | https://en.wikipedia.org/wiki/Shallot | Biology and health sciences | Root vegetables | Plants |
Shallots are extensively cultivated for culinary uses, propagated by offsets. In some regions ("long-season areas"), the offsets are usually planted in autumn (September or October in the Northern Hemisphere). In some other regions, the suggested planting time for the principal crop is early spring (typically in February or the beginning of March in the Northern Hemisphere).
In planting, the tops of the bulbs should be kept a little above ground, and the soil surrounding the bulbs is often drawn away when the roots have taken hold. They come to maturity in summer, although fresh shallots can now be found year-round in supermarkets. Shallots should not be planted on ground recently manured. Shallots suffer damage from leek moth larvae, which mine into the leaves or bulbs of the plant.
Nutrition
A raw shallot is 80% water, 17% carbohydrates, 2.5% protein and contains negligible fat (table). In a reference amount of , raw shallot supplies 72 calories and is a rich source of vitamin B6 (27% of the Daily Value, DV), while providing moderate amounts of manganese (14% DV) and vitamin C (10% DV) (table). No other micronutrients are in significant content.
Uses
Culinary
Shallots are used in cooking. They may be pickled. Finely-sliced deep-fried shallots are used as a condiment in Asian cuisine, often served with porridge. Shallots taste similar to other cultivars of the common onion, but have a milder flavor. Like onions, when sliced, raw shallots release substances that irritate the human eye, resulting in production of tears.
Fresh shallots can be stored in a cool, dry area (0 to 4 °C, 32 to 40 °F, 60 to 70% RH) for six months or longer. Chopped, dried shallots are available.
Europe
In Europe, the Pikant, Atlas, and Ed's Red types of shallots are the most common.
Asia
Shallots are the traditional choice for many dishes in Sri Lankan cuisine, including pol sambola, lunu miris and many meat, fish and vegetable dishes. | Shallot | Wikipedia | 455 | 44346 | https://en.wikipedia.org/wiki/Shallot | Biology and health sciences | Root vegetables | Plants |
In most Indian cuisines, the distinction between onions and shallots is weak; larger varieties of shallot are sometimes confused with small red onions and used interchangeably. Indeed, most parts of India use the regional name for onion interchangeably with shallot (Maharashtra, for instance, where both are called kanda). The southern regions of India distinguish shallots from onions in recipes more often, especially the much loved tiny varieties (about the width of a finger); these are widely used in curries and different types of sambar, a lentil-based dish. Shallots pickled in red vinegar are common in many Indian restaurants, served along with sauces and papad on the condiments tray. They are also used as a home remedy for sore throats, mixed with jaggery or sugar. In Nepal, shallots are used as one of the ingredients for making momo.
In Kashmir shallots are widely used in preparation of Wazwan Kashmiri cuisine, as they add distinct flavor and prevent curry from becoming black, which is common with onions.
In Iran shallots are used in various ways, the most common being grated shallot mixed into dense yogurt, a combination served in almost every restaurant when one orders grills or kebabs. Shallots are also used to make different types of torshi (ترشی), a sour Iranian side dish consisting of a variety of vegetables under vinegar, eaten with main dishes in small quantities. Shallot is also pickled—called shour (شور) in Persian—along with other vegetables to be served as torshi. | Shallot | Wikipedia | 328 | 44346 | https://en.wikipedia.org/wiki/Shallot | Biology and health sciences | Root vegetables | Plants |
In Southeast Asian cuisines, such as those of Indonesia, Vietnam, Thailand, Cambodia, Malaysia, Philippines, Singapore and Brunei, both shallots and garlic are often used as elementary spices. Raw shallots can also accompany cucumbers when pickled in mild vinegar solution. They are also often chopped finely, then fried until golden brown, resulting in tiny crispy shallot chips called bawang goreng (fried shallots) in Indonesian, which can be bought ready-made from groceries and supermarkets. Shallots enhance the flavor of many Southeast Asian dishes, such as fried rice variants. They are also often present in noodle and slaw dishes. Crispy shallot chips are also used in southern Chinese cuisine. In Indonesia, shallots are sometimes pickled and added to several traditional foods; the pickles' sourness is thought to increase the appetite. In the southern Philippines, shallot bulbs and leaves are used to make the popular spicy Maranao condiment called palapa, which is used in the dish Piaparan.
The tubular green leaves of the plant can also be eaten and are very similar to the leaves of spring onions and chives.
Gallery | Shallot | Wikipedia | 235 | 44346 | https://en.wikipedia.org/wiki/Shallot | Biology and health sciences | Root vegetables | Plants |
In physics, Wien's displacement law states that the black-body radiation curve for different temperatures will peak at different wavelengths that are inversely proportional to the temperature. The shift of that peak is a direct consequence of the Planck radiation law, which describes the spectral brightness or intensity of black-body radiation as a function of wavelength at any given temperature. However, it had been discovered by German physicist Wilhelm Wien several years before Max Planck developed that more general equation, and describes the entire shift of the spectrum of black-body radiation toward shorter wavelengths as temperature increases.
Formally, the wavelength version of Wien's displacement law states that the spectral radiance of black-body radiation per unit wavelength, peaks at the wavelength given by:
where is the absolute temperature and is a constant of proportionality called Wien's displacement constant, equal to or .
This is an inverse relationship between wavelength and temperature. So the higher the temperature, the shorter or smaller the wavelength of the thermal radiation. The lower the temperature, the longer or larger the wavelength of the thermal radiation. For visible radiation, hot objects emit bluer light than cool objects. If one is considering the peak of black body emission per unit frequency or per proportional bandwidth, one must use a different proportionality constant. However, the form of the law remains the same: the peak wavelength is inversely proportional to temperature, and the peak frequency is directly proportional to temperature.
There are other formulations of Wien's displacement law, which are parameterized relative to other quantities. For these alternate formulations, the form of the relationship is similar, but the proportionality constant, , differs.
Wien's displacement law may be referred to as "Wien's law", a term which is also used for the Wien approximation.
In "Wien's displacement law", the word displacement refers to how the intensity-wavelength graphs appear shifted (displaced) for different temperatures.
Examples
Wien's displacement law is relevant to some everyday experiences: | Wien's displacement law | Wikipedia | 399 | 44363 | https://en.wikipedia.org/wiki/Wien%27s%20displacement%20law | Physical sciences | Thermodynamics | Physics |
A piece of metal heated by a blow torch first becomes "red hot" as the very longest visible wavelengths appear red, then becomes more orange-red as the temperature is increased, and at very high temperatures would be described as "white hot" as shorter and shorter wavelengths come to predominate the black body emission spectrum. Before it had even reached the red hot temperature, the thermal emission was mainly at longer infrared wavelengths, which are not visible; nevertheless, that radiation could be felt as it warms one's nearby skin.
One easily observes changes in the color of an incandescent light bulb (which produces light through thermal radiation) as the temperature of its filament is varied by a light dimmer. As the light is dimmed and the filament temperature decreases, the distribution of color shifts toward longer wavelengths and the light appears redder, as well as dimmer.
A wood fire at 1500 K puts out peak radiation at about 2000 nanometers. 98% of its radiation is at wavelengths longer than 1000 nm, and only a tiny proportion at visible wavelengths (390–700 nanometers). Consequently, a campfire can keep one warm but is a poor source of visible light.
The effective temperature of the Sun is 5778 Kelvin. Using Wien's law, one finds a peak emission per nanometer (of wavelength) at a wavelength of about 500 nm, in the green portion of the spectrum near the peak sensitivity of the human eye. On the other hand, in terms of power per unit optical frequency, the Sun's peak emission is at 343 THz or a wavelength of 883 nm in the near infrared. In terms of power per percentage bandwidth, the peak is at about 635 nm, a red wavelength. About half of the Sun's radiation is at wavelengths shorter than 710 nm, about the limit of the human vision. Of that, about 12% is at wavelengths shorter than 400 nm, ultraviolet wavelengths, which is invisible to an unaided human eye. A large amount of the Sun's radiation falls in the fairly small visible spectrum and passes through the atmosphere. | Wien's displacement law | Wikipedia | 430 | 44363 | https://en.wikipedia.org/wiki/Wien%27s%20displacement%20law | Physical sciences | Thermodynamics | Physics |
The preponderance of emission in the visible range, however, is not the case in most stars. The hot supergiant Rigel emits 60% of its light in the ultraviolet, while the cool supergiant Betelgeuse emits 85% of its light at infrared wavelengths. With both stars prominent in the constellation of Orion, one can easily appreciate the color difference between the blue-white Rigel (T = 12100 K) and the red Betelgeuse (T ≈ 3800 K). While few stars are as hot as Rigel, stars cooler than the Sun or even as cool as Betelgeuse are very commonplace.
Mammals with a skin temperature of about 300 K emit peak radiation at around 10 μm in the far infrared. This is therefore the range of infrared wavelengths that pit viper snakes and passive IR cameras must sense.
When comparing the apparent color of lighting sources (including fluorescent lights, LED lighting, computer monitors, and photoflash), it is customary to cite the color temperature. Although the spectra of such lights are not accurately described by the black-body radiation curve, a color temperature (the correlated color temperature) is quoted for which black-body radiation would most closely match the subjective color of that source. For instance, the blue-white fluorescent light sometimes used in an office may have a color temperature of 6500 K, whereas the reddish tint of a dimmed incandescent light may have a color temperature (and an actual filament temperature) of 2000 K. Note that the informal description of the former (bluish) color as "cool" and the latter (reddish) as "warm" is exactly opposite the actual temperature change involved in black-body radiation. | Wien's displacement law | Wikipedia | 353 | 44363 | https://en.wikipedia.org/wiki/Wien%27s%20displacement%20law | Physical sciences | Thermodynamics | Physics |
Discovery
The law is named for Wilhelm Wien, who derived it in 1893 based on a thermodynamic argument. Wien considered adiabatic expansion of a cavity containing waves of light in thermal equilibrium. Using Doppler's principle, he showed that, under slow expansion or contraction, the energy of light reflecting off the walls changes in exactly the same way as the frequency. A general principle of thermodynamics is that a thermal equilibrium state, when expanded very slowly, stays in thermal equilibrium.
Wien himself deduced this law theoretically in 1893, following Boltzmann's thermodynamic reasoning. It had previously been observed, at least semi-quantitatively, by an American astronomer, Langley. This upward shift in with is familiar to everyone—when an iron is heated in a fire, the first visible radiation (at around 900 K) is deep red, the lowest frequency visible light. Further increase in causes the color to change to orange then yellow, and finally blue at very high temperatures (10,000 K or more) for which the peak in radiation intensity has moved beyond the visible into the ultraviolet.
The adiabatic principle allowed Wien to conclude that for each mode, the adiabatic invariant energy/frequency is only a function of the other adiabatic invariant, the frequency/temperature. From this, he derived the "strong version" of Wien's displacement law: the statement that the blackbody spectral radiance is proportional to for some function of a single variable. A modern variant of Wien's derivation can be found in the textbook by Wannier and in a paper by E. Buckingham
The consequence is that the shape of the black-body radiation function (which was not yet understood) would shift proportionally in frequency (or inversely proportionally in wavelength) with temperature. When Max Planck later formulated the correct black-body radiation function it did not explicitly include Wien's constant . Rather, the Planck constant was created and introduced into his new formula. From the Planck constant and the Boltzmann constant , Wien's constant can be obtained.
Peak differs according to parameterization
The results in the tables above summarize results from other sections of this article. Percentiles are percentiles of the Planck blackbody spectrum. Only 25 percent of the energy in the black-body spectrum is associated with wavelengths shorter than the value given by the peak-wavelength version of Wien's law. | Wien's displacement law | Wikipedia | 494 | 44363 | https://en.wikipedia.org/wiki/Wien%27s%20displacement%20law | Physical sciences | Thermodynamics | Physics |
Notice that for a given temperature, different parameterizations imply different maximal wavelengths. In particular, the curve of intensity per unit frequency peaks at a different wavelength than the curve of intensity per unit wavelength.
For example, using and parameterization by wavelength, the wavelength for maximal spectral radiance is with corresponding frequency . For the same temperature, but parameterizing by frequency, the frequency for maximal spectral radiance is with corresponding wavelength .
These functions are radiance density functions, which are probability density functions scaled to give units of radiance. The density function has different shapes for different parameterizations, depending on relative stretching or compression of the abscissa, which measures the change in probability density relative to a linear change in a given parameter. Since wavelength and frequency have a reciprocal relation, they represent significantly non-linear shifts in probability density relative to one another.
The total radiance is the integral of the distribution over all positive values, and that is invariant for a given temperature under any parameterization. Additionally, for a given temperature the radiance consisting of all photons between two wavelengths must be the same regardless of which distribution you use. That is to say, integrating the wavelength distribution from to will result in the same value as integrating the frequency distribution between the two frequencies that correspond to and , namely from to . However, the distribution shape depends on the parameterization, and for a different parameterization the distribution will typically have a different peak density, as these calculations demonstrate.
The important point of Wien's law, however, is that any such wavelength marker, including the median wavelength (or, alternatively, the wavelength below which any specified percentage of the emission occurs) is proportional to the reciprocal of temperature. That is, the shape of the distribution for a given parameterization scales with and translates according to temperature, and can be calculated once for a canonical temperature, then appropriately shifted and scaled to obtain the distribution for another temperature. This is a consequence of the strong statement of Wien's law.
Frequency-dependent formulation
For spectral flux considered per unit frequency (in hertz), Wien's displacement law describes a peak emission at the optical frequency given by:
or equivalently
where is a constant resulting from the maximization equation, is the Boltzmann constant, is the Planck constant, and is the absolute temperature. With the emission now considered per unit frequency, this peak now corresponds to a wavelength about 76% longer than the peak considered per unit wavelength. The relevant math is detailed in the next section.
Derivation from Planck's law | Wien's displacement law | Wikipedia | 512 | 44363 | https://en.wikipedia.org/wiki/Wien%27s%20displacement%20law | Physical sciences | Thermodynamics | Physics |
Parameterization by wavelength
Planck's law for the spectrum of black-body radiation predicts the Wien displacement law and may be used to numerically evaluate the constant relating temperature and the peak parameter value for any particular parameterization. Commonly a wavelength parameterization is used and in that case the black body spectral radiance (power per emitting area per solid angle) is:
Differentiating with respect to and setting the derivative equal to zero gives:
which can be simplified to give:
By defining:
the equation becomes one in the single variable x:
which is equivalent to:
This equation is solved by
where is the principal branch of the Lambert W function, and gives . Solving for the wavelength in millimetres, and using kelvins for the temperature yields:
Parameterization by frequency
Another common parameterization is by frequency. The derivation yielding peak parameter value is similar, but starts with the form of Planck's law as a function of frequency :
The preceding process using this equation yields:
The net result is:
This is similarly solved with the Lambert W function:
giving .
Solving for produces:
Parameterization by the logarithm of wavelength or frequency
Using the implicit equation yields the peak in the spectral radiance density function expressed in the parameter radiance per proportional bandwidth. (That is, the density of irradiance per frequency bandwidth proportional to the frequency itself, which can be calculated by considering infinitesimal intervals of (or equivalently ) rather of frequency itself.) This is perhaps a more intuitive way of presenting "wavelength of peak emission". That yields .
Mean photon energy as an alternate characterization
Another way of characterizing the radiance distribution is via the mean photon energy
where is the Riemann zeta function.
The wavelength corresponding to the mean photon energy is given by
Criticism
Marr and Wilkin (2012) contend that the widespread teaching of Wien's displacement law in introductory courses is undesirable, and it would be better replaced by alternate material. They argue that teaching the law is problematic because:
the Planck curve is too broad for the peak to stand out or be regarded as significant;
the location of the peak depends on the parameterization, and they cite several sources as concurring that "that the designation of any peak of the function is not meaningful and should, therefore, be de-emphasized";
the law is not used for determining temperatures in actual practice, direct use of the Planck function being relied upon instead. | Wien's displacement law | Wikipedia | 490 | 44363 | https://en.wikipedia.org/wiki/Wien%27s%20displacement%20law | Physical sciences | Thermodynamics | Physics |
They suggest that the average photon energy be presented in place of Wien's displacement law, as being a more physically meaningful indicator of changes that occur with changing temperature. In connection with this, they recommend that the average number of photons per second be discussed in connection with the Stefan–Boltzmann law. They recommend that the Planck spectrum be plotted as a "spectral energy density per fractional bandwidth distribution," using a logarithmic scale for the wavelength or frequency. | Wien's displacement law | Wikipedia | 96 | 44363 | https://en.wikipedia.org/wiki/Wien%27s%20displacement%20law | Physical sciences | Thermodynamics | Physics |
A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The radiation emitted by a black body in thermal equilibrium with its environment is called black-body radiation. The name "black body" is given because it absorbs all colors of light. In contrast, a white body is one with a "rough surface that reflects all incident rays completely and uniformly in all directions."
A black body in thermal equilibrium (that is, at a constant temperature) emits electromagnetic black-body radiation. The radiation is emitted according to Planck's law, meaning that it has a spectrum that is determined by the temperature alone (see figure at right), not by the body's shape or composition.
An ideal black body in thermal equilibrium has two main properties:
It is an ideal emitter: at every frequency, it emits as much or more thermal radiative energy as any other body at the same temperature.
It is a diffuse emitter: measured per unit area perpendicular to the direction, the energy is radiated isotropically, independent of direction.
Real materials emit energy at a fraction—called the emissivity—of black-body energy levels. By definition, a black body in thermal equilibrium has an emissivity . A source with a lower emissivity, independent of frequency, is often referred to as a gray body.
Constructing black bodies with an emissivity as close to 1 as possible remains a topic of current interest.
In astronomy, the radiation from stars and planets is sometimes characterized in terms of an effective temperature, the temperature of a black body that would emit the same total flux of electromagnetic energy.
Definition
Isaac Newton introduced the notion of a black body in his 1704 book Opticks, with query 6 of the book stating:The idea of a black body originally was introduced by Gustav Kirchhoff in 1860 as follows:
A more modern definition drops the reference to "infinitely small thicknesses":
Idealizations
This section describes some concepts developed in connection with black bodies. | Black body | Wikipedia | 417 | 44364 | https://en.wikipedia.org/wiki/Black%20body | Physical sciences | Thermodynamics | Physics |
Cavity with a hole
A widely used model of a black surface is a small hole in a cavity with walls that are opaque to radiation. Radiation incident on the hole will pass into the cavity, and is very unlikely to be re-emitted if the cavity is large. Lack of any re-emission, means that the hole is behaving like a perfect black surface. The hole is not quite a perfect black surface—in particular, if the wavelength of the incident radiation is greater than the diameter of the hole, part will be reflected. Similarly, even in perfect thermal equilibrium, the radiation inside a finite-sized cavity will not have an ideal Planck spectrum for wavelengths comparable to or larger than the size of the cavity.
Suppose the cavity is held at a fixed temperature T and the radiation trapped inside the enclosure is at thermal equilibrium with the enclosure. The hole in the enclosure will allow some radiation to escape. If the hole is small, radiation passing in and out of the hole has negligible effect upon the equilibrium of the radiation inside the cavity. This escaping radiation will approximate black-body radiation that exhibits a distribution in energy characteristic of the temperature T and does not depend upon the properties of the cavity or the hole, at least for wavelengths smaller than the size of the hole. See the figure in the Introduction for the spectrum as a function of the frequency of the radiation, which is related to the energy of the radiation by the equation E = hf, with E = energy, h = Planck constant, f = frequency.
At any given time the radiation in the cavity may not be in thermal equilibrium, but the second law of thermodynamics states that if left undisturbed it will eventually reach equilibrium, although the time it takes to do so may be very long. Typically, equilibrium is reached by continual absorption and emission of radiation by material in the cavity or its walls. Radiation entering the cavity will be "thermalized" by this mechanism: the energy will be redistributed until the ensemble of photons achieves a Planck distribution. The time taken for thermalization is much faster with condensed matter present than with rarefied matter such as a dilute gas. At temperatures below billions of Kelvin, direct photon–photon interactions are usually negligible compared to interactions with matter. Photons are an example of an interacting boson gas, and as described by the H-theorem, under very general conditions any interacting boson gas will approach thermal equilibrium. | Black body | Wikipedia | 497 | 44364 | https://en.wikipedia.org/wiki/Black%20body | Physical sciences | Thermodynamics | Physics |
Transmission, absorption, and reflection
A body's behavior with regard to thermal radiation is characterized by its transmission τ, absorption α, and reflection ρ.
The boundary of a body forms an interface with its surroundings, and this interface may be rough or smooth. A nonreflecting interface separating regions with different refractive indices must be rough, because the laws of reflection and refraction governed by the Fresnel equations for a smooth interface require a reflected ray when the refractive indices of the material and its surroundings differ. A few idealized types of behavior are given particular names:
An opaque body is one that transmits none of the radiation that reaches it, although some may be reflected. That is, τ = 0 and α + ρ = 1.
A transparent body is one that transmits all the radiation that reaches it. That is, τ = 1 and α = ρ = 0.
A grey body is one where α, ρ and τ are constant for all wavelengths; this term also is used to mean a body for which α is temperature- and wavelength-independent.
A white body is one for which all incident radiation is reflected uniformly in all directions: τ = 0, α = 0, and ρ = 1.
For a black body, τ = 0, α = 1, and ρ = 0. Planck offers a theoretical model for perfectly black bodies, which he noted do not exist in nature: besides their opaque interior, they have interfaces that are perfectly transmitting and non-reflective.
Kirchhoff's perfect black bodies
Kirchhoff in 1860 introduced the theoretical concept of a perfect black body with a completely absorbing surface layer of infinitely small thickness, but Planck noted some severe restrictions upon this idea. Planck noted three requirements upon a black body: the body must (i) allow radiation to enter but not reflect; (ii) possess a minimum thickness adequate to absorb the incident radiation and prevent its re-emission; (iii) satisfy severe limitations upon scattering to prevent radiation from entering and bouncing back out. As a consequence, Kirchhoff's perfect black bodies that absorb all the radiation that falls on them cannot be realized in an infinitely thin surface layer, and impose conditions upon scattering of the light within the black body that are difficult to satisfy.
Realizations
A realization of a black body refers to a real world, physical embodiment. Here are a few. | Black body | Wikipedia | 477 | 44364 | https://en.wikipedia.org/wiki/Black%20body | Physical sciences | Thermodynamics | Physics |
Cavity with a hole
In 1898, Otto Lummer and Ferdinand Kurlbaum published an account of their cavity radiation source. Their design has been used largely unchanged for radiation measurements to the present day. It was a hole in the wall of a platinum box, divided by diaphragms, with its interior blackened with iron oxide. It was an important ingredient for the progressively improved measurements that led to the discovery of Planck's law. A version described in 1901 had its interior blackened with a mixture of chromium, nickel, and cobalt oxides. | Black body | Wikipedia | 111 | 44364 | https://en.wikipedia.org/wiki/Black%20body | Physical sciences | Thermodynamics | Physics |
A typewriter is a mechanical or electromechanical machine for typing characters. Typically, a typewriter has an array of keys, and each one causes a different single character to be produced on paper by striking an inked ribbon selectively against the paper with a type element. Thereby, the machine produces a legible written document composed of ink and paper. By the end of the 19th century, a person who used such a device was also referred to as a typewriter.
The first commercial typewriters were introduced in 1874, but did not become common in offices in the United States until after the mid-1880s. The typewriter quickly became an indispensable tool for practically all writing other than personal handwritten correspondence. It was widely used by professional writers, in offices, in business correspondence in private homes, and by students preparing written assignments.
Typewriters were a standard fixture in most offices up to the 1980s. After that, they began to be largely supplanted by personal computers running word processing software. Nevertheless, typewriters remain common in some parts of the world. For example, typewriters are still used in many Indian cities and towns, especially in roadside and legal offices, due to a lack of continuous, reliable electricity.
The QWERTY keyboard layout, developed for typewriters in the 1870s, remains the de facto standard for English-language computer keyboards. The origins of this layout still need to be clarified. Similar typewriter keyboards, with layouts optimised for other languages and orthographies, emerged soon afterward, and their layouts have also become standard for computer keyboards in their respective markets.
History
Although many modern typewriters have one of several similar designs, their invention was incremental, developed by numerous inventors working independently or in competition with each other over a series of decades. As with the automobile, the telephone, and telegraph, several people contributed insights and inventions that eventually resulted in ever more commercially successful instruments. Historians have estimated that some form of the typewriter was invented 52 times as thinkers and tinkerers tried to come up with a workable design.
Some early typing instruments include: | Typewriter | Wikipedia | 437 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
In 1575, an Italian printmaker, Francesco Rampazetto, invented the , a machine to impress letters in papers.
In 1714, Henry Mill obtained a patent in Britain for a machine that, from the patent, appears to have been similar to a typewriter. The patent shows that this machine was created: "[he] hath by his great study and paines & expence invented and brought to perfection an artificial machine or method for impressing or transcribing of letters, one after another, as in writing, whereby all writing whatsoever may be engrossed in paper or parchment so neat and exact as not to be distinguished from print; that the said machine or method may be of great use in settlements and public records, the impression being deeper and more lasting than any other writing, and not to be erased or counterfeited without manifest discovery."
In 1802, Italian Agostino Fantoni developed a particular typewriter to enable his blind sister to write.
Between 1801 and 1808, Italian Pellegrino Turri invented a typewriter for his blind friend Countess Carolina Fantoni da Fivizzano.
In 1823, Italian Pietro Conti da Cilavegna invented a new model of the typewriter, the , also known as .
In 1829, American William Austin Burt patented a machine called the "Typographer" which, in common with many other early machines, is listed as the "first typewriter". The London Science Museum describes it merely as "the first writing mechanism whose invention was documented", but even that claim may be excessive since Turri's invention pre-dates it.
By the mid-19th century, the increasing pace of business communication had created a need to mechanize the writing process. Stenographers and telegraphers could take down information at rates up to 130 words per minute, whereas a writer with a pen was limited to a maximum of 30 words per minute (the 1853 speed record).
From 1829 to 1870, many printing or typing machines were patented by inventors in Europe and America, but none went into commercial production. | Typewriter | Wikipedia | 427 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
American Charles Thurber developed multiple patents, of which his first in 1843 was created as an aid to blind people, such as the 1845 Chirographer.
In 1855, the Italian Giuseppe Ravizza created a prototype typewriter called Cembalo scrivano o macchina da scrivere a tasti ("Scribe harpsichord, or machine for writing with keys"). It was an advanced machine that let the user see the writing as it was typed.
In 1861, Father Francisco João de Azevedo, a Brazilian priest, made his typewriter with basic materials and tools, such as wood and knives. In that same year, the Brazilian emperor D. Pedro II, presented a gold medal to Father Azevedo for this invention. Many Brazilian people, as well as the Brazilian federal government recognize Fr. Azevedo as the inventor of the typewriter, a claim that has been the subject of some controversy.
In 1865, John Pratt, of Centre, Alabama (US), built a machine called the Pterotype which appeared in an 1867 Scientific American article and inspired other inventors.
Between 1864 and 1867, , a carpenter from South Tyrol (then part of Austria) developed several models and a fully functioning prototype typewriter in 1867.
Hansen Writing Ball
In 1865, Rev. Rasmus Malling-Hansen of Denmark invented the Hansen Writing Ball, which went into commercial production in 1870 and was the first commercially sold typewriter. It was a success in Europe and was reported as being used in offices on the European continent as late as 1909.
Malling-Hansen used a solenoid escapement to return the carriage on some of his models, which makes him a candidate for the title of inventor of the first "electric" typewriter.
The Hansen Writing Ball was produced with only upper-case characters. The Writing Ball was a template for inventor Frank Haven Hall to create a derivative that would produce letter prints cheaper and faster. | Typewriter | Wikipedia | 392 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Malling-Hansen developed his typewriter further through the 1870s and 1880s and made many improvements, but the writing head remained the same. On the first model of the writing ball from 1870, the paper was attached to a cylinder inside a wooden box. In 1874, the cylinder was replaced by a carriage, moving beneath the writing head. Then, in 1875, the well-known "tall model" was patented, which was the first of the writing balls that worked without electricity. Malling-Hansen attended the world exhibitions in Vienna in 1873 and Paris in 1878 and he received the first-prize for his invention at both exhibitions.
Sholes and Glidden typewriter
The first typewriter to be commercially successful was patented in 1868 by Americans Christopher Latham Sholes, Frank Haven Hall, Carlos Glidden and Samuel W. Soule in Milwaukee, Wisconsin, although Sholes soon disowned the machine and refused to use or even recommend it. The working prototype was made by clock-maker and machinist Matthias Schwalbach. Hall, Glidden and Soule sold their shares in the patent (US 79,265) to Sholes and James Densmore, who made an agreement with E. Remington and Sons (then famous as a manufacturer of sewing machines) to commercialize the machine as the Sholes and Glidden Type-Writer. This was the origin of the term typewriter.
Remington began production of its first typewriter on March 1, 1873, in Ilion, New York. It had a QWERTY keyboard layout, which, because of the machine's success, was slowly adopted by other typewriter manufacturers. As with most other early typewriters, because the typebars strike upwards, the typist could not see the characters as they were typed.
Index typewriter
The index typewriter came into the market in the early 1880s. The index typewriter uses a pointer or stylus to choose a letter from an index. The pointer is mechanically linked so that the letter chosen could then be printed, most often by the activation of a lever. | Typewriter | Wikipedia | 424 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
The index typewriter was briefly popular in niche markets. Although they were slower than keyboard type machines, they were mechanically simpler and lighter. They were therefore marketed as being suitable for travellers and, because they could be produced more cheaply than keyboard machines, as budget machines for users who needed to produce small quantities of typed correspondence. For example, the Simplex Typewriter Company made index typewriters for 1/40 the price of a Remington typewriter.
The index typewriter's niche appeal however soon disappeared as, on the one hand new keyboard typewriters became lighter and more portable, and on the other refurbished second-hand machines began to become available. The last widely available western index machine was the Mignon typewriter produced by AEG which was produced until 1934. Considered one of the very best of the index typewriters, part of the Mignon's popularity was that it featured interchangeable indexes as well as type, fonts and character sets. This is something very few keyboard machines were capable of--and only at considerable added cost.
Although they were pushed out of the market in most of the world by keyboard machines, successful Japanese and Chinese typewriters typewriters are of the index type--albeit with a very much larger index and number of type elements.
Embossing tape label makers are the most common index typewriters today, and perhaps the most common typewriters of any kind still being manufactured.
The platen was mounted on a carriage that moved horizontally to the left, automatically advancing the typing position, after each character was typed. The carriage-return lever at the far left was then pressed to the right to return the carriage to its starting position and rotating the platen to advance the paper vertically. A small bell was struck a few characters before the right hand margin was reached to warn the operator to complete the word and then use the carriage-return lever.
Other typewriters | Typewriter | Wikipedia | 390 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
1884 – Hammond "Ideal" typewriter with case, by Hammond Typewriter Company Limited, United States. Despite an unusual, curved keyboard (see picture in citation), the Hammond became popular because of its superior print quality and changeable typeface. Invented by James Hammond of Boston, Massachusetts in 1880, and commercially released in 1884. The type is carried on a pair of interchangeable rotating sectors, one controlled by each half of the keyboard. A small hammer pushes the paper against the ribbon and type sector to print each character. The mechanism was later adapted to give a straight QWERTY keyboard and proportional spacing.
1888 – Fitch typewriter – Made by the Fitch Typewriter Company, Brooklyn, N.Y. and later in the UK with a slightly different look. Operators of the early typewriters had to work "blind": the typed text emerged only after several lines had been completed or the carriage was lifted to look underneath at the page. The Fitch was one of the first machines to allow prompt correction of mistakes with its visible writing; it was said to be the second machine operating on the visible writing system. The typebars were positioned behind the paper and the writing area faced upwards so that the result could be seen instantly. A curved frame kept the emerging paper from obscuring the keyboard, but the Fitch was soon eclipsed by machines in which the paper could be fed more conveniently at the rear.
1893 – Gardner typewriter. This typewriter, patented by Mr J Gardner in 1893, was an attempt to reduce the size and cost. Although it prints 84 symbols, it has only 14 keys and two change-case keys. Several characters are indicated on each key and the character printed is determined by the position of the case keys, which choose one of six cases.
1896 – The "Underwood 1 typewriter, 10" Pica, No. 990". This was the first typewriter with a typing area fully visible to the typist until a key is struck. These features, copied by all subsequent typewriters, allowed the typist to see and if necessary correct the typing as it proceeded. The mechanism was developed in the US by Franz X. Wagner from about 1892 and taken up, in 1895, by John T. Underwood (1857–1937), a producer of office supplies. | Typewriter | Wikipedia | 471 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Standardization
By about 1910, the "manual" or "mechanical" typewriter had reached a somewhat standardized design. There were minor variations from one manufacturer to another, but most typewriters followed the concept that each key was attached to a typebar that had the corresponding letter molded, in reverse, into its striking head. When a key was struck briskly and firmly, the typebar hit a ribbon (usually made of inked fabric), making a printed mark on the paper wrapped around a cylindrical platen.
The platen was mounted on a carriage that moved horizontally to the left, automatically advancing the typing position, after each character was typed. The carriage-return lever at the far left was then pressed to the right to return the carriage to its starting position and rotating the platen to advance the paper vertically. A small bell was struck a few characters before the right hand margin was reached to warn the operator to complete the word and then use the carriage-return lever. Typewriters for languages written right-to-left operate in the opposite direction.
By 1900, notable typewriter manufacturers included E. Remington and Sons, IBM, Godrej, Imperial Typewriter Company, Oliver Typewriter Company, Olivetti, Royal Typewriter Company, Smith Corona, Underwood Typewriter Company, Facit, Adler, and Olympia-Werke.
After the market had matured under the market dominance of large companies from Britain, Europe and the United States—but before the advent of daisywheel and electronic machines—the typewriter market faced strong competition from less expensive typewriters from Asia, including Brother Industries and Silver Seiko Ltd. of Japan.
Frontstriking
In most of the early typewriters, the typebars struck upward against the paper, pressed against the bottom of the platen, so the typist could not see the text as it was typed. What was typed was not visible until a carriage return caused it to scroll into view.
The difficulty with any other arrangement was ensuring the typebars fell back into place reliably when the key was released. This was eventually achieved with various ingenious mechanical designs and so-called "visible typewriters" which used frontstriking, in which the typebars struck forward against the front side of the platen, became standard. One of the first was the Daugherty Visible, introduced in 1893, which also introduced the four-bank keyboard that became standard, although the Underwood which came out two years later was the first major typewriter with these features. | Typewriter | Wikipedia | 512 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Shift key
A significant innovation was the shift key, introduced with the Remington No. 2 in 1878. This key physically "shifted" either the basket of typebars, in which case the typewriter is described as "basket shift", or the paper-holding carriage, in which case the typewriter is described as "carriage shift". Either mechanism caused a different portion of the typebar to come in contact with the ribbon/platen.
The result is that each typebar could type two different characters, cutting the number of keys and typebars in half (and simplifying the internal mechanisms considerably). The obvious use for this was to allow letter keys to type both upper and lower case, but normally the number keys were also duplexed, allowing access to special symbols such as percent, , and ampersand, .
Before the shift key, typewriters had to have a separate key and typebar for upper-case letters; in essence, the typewriter had two keyboards, one above the other. With the shift key, manufacturing costs (and therefore purchase price) were greatly reduced, and typist operation was simplified; both factors contributed greatly to mass adoption of the technology.
Three-bank typewriters
Certain models further reduced the number of keys and typebars by making each key perform three functions – each typebar could type three different characters. These little three-row machines were portable and could be used by journalists.
Such three-row machines were popular with WWI journalists because they were lighter and more compact than four-bank typewriters, while they could type just as fast and use just as many symbols.
Such three-row machines, such as the Bar-Let and the Corona No. 3 Typewriter have two separate shift keys, a "CAP" shift (for uppercase) and a "FIG" shift (for numbers and symbols).
The Murray code was developed for a teletypewriter with a similar three-row typewriter keyboard.
Tab key | Typewriter | Wikipedia | 406 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
To facilitate typewriter use in business settings, a tab (tabulator) key was added in the late nineteenth century. Before using the key, the operator had to set mechanical "tab stops", pre-designated locations to which the carriage would advance when the tab key was pressed. This facilitated the typing of columns of numbers, freeing the operator from the need to manually position the carriage. The first models had one tab stop and one tab key; later ones allowed as many stops as desired, and sometimes had multiple tab keys, each of which moved the carriage a different number of spaces ahead of the decimal point (the tab stop), to facilitate the typing of columns with numbers of different length ($1.00, $10.00, $100.00, etc.)
Dead keys
Languages such as French, Spanish, and German required diacritics, special signs attached to or on top of the base letter: for example, a combination of the acute accent plus produced ; plus produced . In metal typesetting, , , and others were separate sorts. With mechanical typewriters, the number of whose characters (sorts) was constrained by the physical limits of the machine, the number of keys required was reduced by the use of dead keys. Diacritics such as (acute accent) would be assigned to a dead key, which did not move the platen forward, permitting another character to be imprinted at the same location; thus a single dead key such as the acute accent could be combined with ,,, and to produce ,,, and , reducing the number of sorts needed from 5 to 1. The typebars of "normal" characters struck a rod as they moved the metal character desired toward the ribbon and platen, and each rod depression moved the platen forward the width of one character. Dead keys had a typebar shaped so as not to strike the rod.
Character sizes
In English-speaking countries, ordinary typewriters printing fixed-width characters were standardized to print six horizontal lines per vertical inch, and had either of two variants of character width, one called pica for ten characters per horizontal inch and the other elite, for twelve. This differed from the use of these terms in printing, where pica is a linear unit (approximately of an inch) used for any measurement, the most common one being the height of a typeface. | Typewriter | Wikipedia | 482 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Color
Some ribbons were inked in black and red stripes, each being half the width and running the entire length of the ribbon. A lever on most machines allowed switching between colors, which was useful for bookkeeping entries where negative amounts were highlighted in red. The red color was also used on some selected characters in running text, for emphasis. When a typewriter had this facility, it could still be fitted with a solid black ribbon; the lever was then used to switch to fresh ribbon when the first stripe ran out of ink. Some typewriters also had a third position which stopped the ribbon being struck at all. This enabled the keys to hit the paper unobstructed, and was used for cutting stencils for stencil duplicators (aka mimeograph machines).
"Noiseless" designs
The first typewriter to have the sliding type bars (laid out horizontally like a fan) that enable a typewriter to be "noiseless" was the American made Rapid which appeared briefly on the market in 1890. The Rapid also had the remarkable ability for the typist to have entire control of the carriage by manipulation of the keyboard alone. The two keys that achieve this are positioned at the top of the keyboard (seen in the detail image below). They are a "Lift" key that advances the paper, on the platen, to the next line and a "Return" key that causes the carriage to automatically swing back to the right, ready for one to type the new line. So an entire page could be typed without one's hands leaving the keyboard.
In the early part of the 20th century, a typewriter was marketed under the name Noiseless and advertised as "silent". It was developed by Wellington Parker Kidder and the first model was marketed by the Noiseless Typewriter Company in 1917. Noiseless portables sold well in the 1930s and 1940s, and noiseless standards continued to be manufactured until the 1960s.
In a conventional typewriter the type bar reaches the end of its travel simply by striking the ribbon and paper. The Noiseless, developed by Kidder, has a complex lever mechanism that decelerates the type bar mechanically before pressing it against the ribbon and paper in an attempt to dampen the noise. | Typewriter | Wikipedia | 457 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Electric designs
Although electric typewriters would not achieve widespread popularity until nearly a century later, the basic groundwork for the electric typewriter was laid by the Universal Stock Ticker, invented by Thomas Edison in 1870. This device remotely printed letters and numbers on a stream of paper tape from input generated by a specially designed typewriter at the other end of a telegraph line.
Early electric models
Some electric typewriters were patented in the 19th century, but the first machine known to be produced in series is the Cahill of 1900.
Another electric typewriter was produced by the Blickensderfer Manufacturing Company, of Stamford, Connecticut, in 1902. Like the manual Blickensderfer typewriters, it used a cylindrical typewheel rather than individual typebars. The machine was produced in several variants but apparently not a commercial success, having come to market ahead of its time, before ubiquitous electrification.
The next step in the development of the electric typewriter came in 1910, when Charles and Howard Krum filed a patent for the first practical teletypewriter. The Krums' machine, named the Morkrum Printing Telegraph, used a typewheel rather than individual typebars. This machine was used for the first commercial teletypewriter system on Postal Telegraph Company lines between Boston and New York City in 1910.
James Fields Smathers of Kansas City invented what is considered the first practical power-operated typewriter in 1914. In 1920, after returning from Army service, he produced a successful model and in 1923 turned it over to the Northeast Electric Company of Rochester for development. Northeast was interested in finding new markets for their electric motors and developed Smathers's design so that it could be marketed to typewriter manufacturers, and from 1925 Remington Electric typewriters were produced powered by Northeast's motors.
After some 2,500 electric typewriters had been produced, Northeast asked Remington for a firm contract for the next batch. However, Remington was engaged in merger talks, which would eventually result in the creation of Remington Rand and no executives were willing to commit to a firm order. Northeast instead decided to enter the typewriter business for itself, and in 1929 produced the first Electromatic Typewriter. | Typewriter | Wikipedia | 447 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
In 1928, Delco, a division of General Motors, purchased Northeast Electric, and the typewriter business was spun off as Electromatic Typewriters, Inc. In 1933, Electromatic was acquired by IBM, which then spent $1 million on a redesign of the Electromatic Typewriter, launching the IBM Electric Typewriter Model 01.
In 1931, an electric typewriter was introduced by Varityper Corporation. It was called the Varityper, because a narrow cylinder-like wheel could be replaced to change the font.
In 1941, IBM announced the Electromatic Model 04 electric typewriter, featuring the revolutionary concept of proportional spacing. By assigning varied rather than uniform spacing to different sized characters, the Type 4 recreated the appearance of a typeset page, an effect that was further enhanced by including the 1937 innovation of carbon-film ribbons that produced clearer, sharper words on the page.
IBM Selectric
IBM introduced the IBM Selectric typewriter in 1961, which replaced the typebars with a spherical element (or typeball) slightly smaller than a golf ball, with reverse-image letters molded into its surface. The Selectric used a system of latches, metal tapes, and pulleys driven by an electric motor to rotate the ball into the correct position and then strike it against the ribbon and platen. The typeball moved laterally in front of the paper, instead of the previous designs using a platen-carrying carriage moving the paper across a stationary print position.
Due to the physical similarity, the typeball was sometimes referred to as a "golfball". The typeball design had many advantages, especially the elimination of "jams" (when more than one key was struck at once and the typebars became entangled) and in the ability to change the typeball, allowing multiple fonts to be used in a single document.
The IBM Selectric became a commercial success, dominating the office typewriter market for at least two decades. IBM also gained an advantage by marketing more heavily to schools than did Remington, with the idea that students who learned to type on a Selectric would later choose IBM typewriters over the competition in the workplace as businesses replaced their old manual models. | Typewriter | Wikipedia | 449 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Later models of IBM Executives and Selectrics replaced inked fabric ribbons with "carbon film" ribbons that had a dry black or colored powder on a clear plastic tape. These could be used only once, but later models used a cartridge that was simple to replace. A side effect of this technology was that the text typed on the machine could be easily read from the used ribbon, raising issues where the machines were used for preparing classified documents (ribbons had to be accounted for to ensure that typists did not carry them from the facility).
A variation known as "Correcting Selectrics" introduced a correction feature, later imitated by competing machines, where a sticky tape in front of the carbon film ribbon could remove the black-powdered image of a typed character, eliminating the need for little bottles of white dab-on correction fluid and for hard erasers that could tear the paper. These machines also introduced selectable "pitch" so that the typewriter could be switched between pica type (10 characters per inch) and elite type (12 per inch), even within one document. Even so, all Selectrics were monospaced – each character and letterspace was allotted the same width on the page, from a capital "W" to a period. IBM did produce a successful typebar-based machine with five levels of proportional spacing, called the IBM Executive.
The only fully electromechanical Selectric Typewriter with fully proportional spacing and which used a Selectric type element was the expensive Selectric Composer, which was capable of right-margin justification (typing each line twice was required, once to calculate and again to print) and was considered a typesetting machine rather than a typewriter. Composer typeballs physically resembled those of the Selectric typewriter but were not interchangeable.In addition to its electronic successors, the Magnetic Tape Selectric Composer (MT/SC), the Mag Card Selectric Composer, and the Electronic Selectric Composer, IBM also made electronic typewriters with proportional spacing using the Selectric element that were considered typewriters or word processors instead of typesetting machines.
The first of these was the relatively obscure Mag Card Executive, which used 88-character elements. Later, some of the same typestyles used for it were used on the 96-character elements used on the IBM Electronic Typewriter 50 and the later models 65 and 85. | Typewriter | Wikipedia | 488 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
By 1970, as offset printing began to replace letterpress printing, the Composer would be adapted as the output unit for a phototypesetting system. The system included a computer-driven input station to capture the key strokes on magnetic tape and insert the operator's format commands, and a Composer unit to read the tape and produce the formatted text for photo reproduction.
The IBM 2741 terminal was a popular example of a Selectric-based computer terminal, and similar mechanisms were employed as the console devices for many IBM System/360 computers. These mechanisms used "ruggedized" designs compared to those in standard office typewriters.
Later electric models
Some of IBM's advances were later adopted in less expensive machines from competitors. For example, Smith-Corona electric typewriters introduced in 1973 switched to interchangeable Coronamatic (SCM-patented) ribbon cartridges. including fabric, film, erasing, and two-color versions. At about the same time, the advent of photocopying meant that carbon copies, correction fluid and erasers were less and less necessary; only the original need be typed, and photocopies made from it.
Electronic typewriters
The final major development of the typewriter was the electronic typewriter. Most of these replaced the typeball with a plastic or metal daisy wheel mechanism (a disk with the letters molded on the outside edge of the "petals"). The daisy wheel concept first emerged in printers developed by Diablo Systems in the 1970s. The first electronic daisywheel typewriter marketed in the world (in 1976) is the Olivetti Tes 501, and subsequently in 1978, the Olivetti ET101 (with function display) and Olivetti TES 401 (with text display and floppy disk for memory storage). This has allowed Olivetti to maintain the world record in the design of electronic typewriters, proposing increasingly advanced and performing models in the following years. | Typewriter | Wikipedia | 386 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Unlike the Selectrics and earlier models, these really were "electronic" and relied on integrated circuits and electromechanical components. These typewriters were sometimes called display typewriters, dedicated word processors or word-processing typewriters, though the latter term was also frequently applied to less sophisticated machines that featured only a tiny, sometimes just single-row display. Sophisticated models were also called word processors, though today that term almost always denotes a type of software program. Manufacturers of such machines included Olivetti (TES501, first totally electronic Olivetti word processor with daisywheel and floppy disk in 1976; TES621 in 1979 etc.), Brother (Brother WP1 and WP500 etc., where WP stood for word processor), Canon (Canon Cat), Smith-Corona (PWP, i.e. Personal Word Processor line) and Philips/Magnavox (VideoWriter).
Decline
The pace of change was so rapid that it was common for clerical staff to have to learn several new systems, one after the other, in just a few years. While such rapid change is commonplace today, and is taken for granted, this was not always so; in fact, typewriting technology changed very little in its first 80 or 90 years.
Due to falling sales, IBM sold its typewriter division in 1991 to the newly formed Lexmark, completely exiting from a market it once dominated.
The increasing dominance of personal computers, desktop publishing, the introduction of low-cost, truly high-quality laser and inkjet printer technologies, and the pervasive use of web publishing, email, text messaging, and other electronic communication techniques have largely replaced typewriters in the United States. Still, , typewriters continued to be used by a number of government agencies and other institutions in the US, where they are primarily used to fill preprinted forms. According to a Boston typewriter repairman quoted by The Boston Globe, "Every maternity ward has a typewriter, as well as funeral homes". | Typewriter | Wikipedia | 415 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
A rather specialized market for typewriters exists due to the regulations of many correctional systems in the US, where prisoners are prohibited from having computers or telecommunication equipment, but are allowed to own typewriters. The Swintec corporation (headquartered in Moonachie, New Jersey), which, as of 2011, still produced typewriters at its overseas factories (in Japan, Indonesia, and/or Malaysia), manufactures a variety of typewriters for use in prisons, made of clear plastic (to make it harder for prisoners to hide prohibited items inside it). As of 2011, the company had contracts with prisons in 43 US states.
In April 2011, Godrej and Boyce, a Mumbai-based manufacturer of mechanical typewriters, closed its doors, leading to a flurry of news reports that the "world's last typewriter factory" had shut down. The reports were quickly contested, with opinions settling to agree that it was indeed the world's last producer of manual typewriters.
In November 2012, Brother's UK factory manufactured what it claimed to be the last typewriter ever made in the UK; the typewriter was donated to the London Science Museum.
Russian typewriters use Cyrillic, which has made the ongoing Azerbaijani reconversion from Cyrillic to Latin alphabet more difficult. In 1997, the government of Turkey offered to donate western typewriters to the Republic of Azerbaijan in exchange for more zealous and exclusive promotion of the Latin alphabet for the Azerbaijani language; this offer, however, was declined.
In Latin America and Africa, mechanical typewriters are still common because they can be used without electrical power. In Latin America, the typewriters used are most often Brazilian models; Brazil continues to produce mechanical (Facit) and electronic (Olivetti) typewriters to the present day.
The early 21st century saw revival of interest in typewriters among certain subcultures, including makers, steampunks, hipsters, and street poets.
Correction technologies
According to the standards taught in secretarial schools in the mid-20th century, a business letter was supposed to have no mistakes and no visible corrections.
Typewriter erasers | Typewriter | Wikipedia | 442 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
The traditional erasing method involved the use of a special typewriter eraser made of hard rubber that contained an abrasive material. Some were thin, flat disks, pink or gray, approximately in diameter by thick, with a brush attached from the center, while others looked like pink pencils, with a sharpenable eraser at the "lead" end and a stiff nylon brush at the other end. Either way, these tools made possible erasure of individual typed letters. Business letters were typed on heavyweight, high-rag-content bond paper, not merely to provide a luxurious appearance, but also to stand up to erasure.
Typewriter eraser brushes were necessary for clearing eraser crumbs and paper dust, and using the brush properly was an important element of typewriting skill; if erasure detritus fell into the typewriter, a small buildup could cause the typebars to jam in their narrow supporting grooves.
Erasing shield
Erasing a set of carbon copies was particularly difficult, and called for the use of a device called an erasing shield or eraser shield (a thin stainless-steel rectangle about with several tiny holes in it) to prevent the pressure of erasing on the upper copies from producing carbon smudges on the lower copies. To correct copies, typists had to go from one carbon copy layer to the next carbon copy layer, trying not to get their fingers dirty as they leafed through the carbon papers, and moving and repositioning the eraser shield and eraser for each copy.
Erasable bond
Paper companies produced a special form of typewriter paper called erasable bond (for example, Eaton's Corrasable Bond). This incorporated a thin layer of material that prevented ink from penetrating and was relatively soft and easy to remove from the page. An ordinary soft pencil eraser could quickly produce perfect erasures on this kind of paper. However, the same characteristics that made the paper erasable made the characters subject to smudging due to ordinary friction and deliberate alteration after the fact, making it unacceptable for business correspondence, contracts, or any archival use.
Correction fluid | Typewriter | Wikipedia | 432 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
In the 1950s and 1960s, correction fluid made its appearance, under brand names such as Liquid Paper, Wite-Out and Tipp-Ex; it was invented by Bette Nesmith Graham. Correction fluid was a kind of opaque, white, fast-drying paint that produced a fresh white surface onto which, when dry, a correction could be retyped. However, when held to the light, the covered-up characters were visible, as was the patch of dry correction fluid (which was never perfectly flat, and frequently not a perfect match for the color, texture, and luster of the surrounding paper). The standard trick for solving this problem was photocopying the corrected page, but this was possible only with high quality photocopiers.
A different fluid was available for correcting stencils. It sealed up the stencil ready for retyping but did not attempt to color match.
Legacy
Keyboard layouts
QWERTY
The 1874 Sholes & Glidden typewriters established the "QWERTY" layout for the letter keys. During the period in which Sholes and his colleagues were experimenting with this invention, other keyboard arrangements were apparently tried, but these are poorly documented. The QWERTY layout of keys has become the de facto standard for English-language typewriter and computer keyboards. Other languages written in the Latin alphabet sometimes use variants of the QWERTY layouts, such as the French AZERTY, the Italian QZERTY and the German QWERTZ layouts.
The QWERTY layout is not the most efficient layout possible for the English language. Touch-typists are required to move their fingers between rows to type the most common letters. Although the QWERTY keyboard was the most commonly used layout in typewriters, a better, less strenuous keyboard was being searched for throughout the late 1900s.
One popular but incorrect explanation for the QWERTY arrangement is that it was designed to reduce the likelihood of internal clashing of typebars by placing commonly used combinations of letters farther from each other inside the machine. | Typewriter | Wikipedia | 423 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Other layouts for English
A number of radically different layouts such as Dvorak have been proposed to reduce the perceived inefficiencies of QWERTY, but none have been able to displace the QWERTY layout; their proponents claim considerable advantages, but so far none has been widely used. The Blickensderfer typewriter with its DHIATENSOR layout may have possibly been the first attempt at optimizing the keyboard layout for efficiency advantages.
On modern keyboards, the exclamation point is the shifted character on the 1 key, because these were the last characters to become "standard" on keyboards. Holding the spacebar down usually suspended the carriage advance mechanism (a so-called "dead key" feature), allowing one to superimpose multiple keystrikes on a single location. The ¢ symbol (meaning cents) was located above the number 6 on American electric typewriters, whereas ANSI-INCITS-standard computer keyboards have ^ instead.
Keyboards for other languages
The keyboards for other Latin languages are broadly similar to QWERTY but are optimised for the relevant orthography. In addition to some changes in the order of letters, perhaps the most obvious is the presence of precomposed characters and diacritics.
Many non-Latin alphabets have keyboard layouts that have nothing to do with QWERTY. The Russian layout, for instance, puts the common trigrams ыва, про, and ить on adjacent keys so that they can be typed by rolling the fingers.
Typewriters were also made for East Asian languages with thousands of characters, such as Chinese or Japanese. They were not easy to operate, but professional typists used them for a long time until the development of electronic word processors and laser printers in the 1980s.
Typewriter conventions
A number of typographical conventions stem from the typewriter's characteristics and limitations. For example, the QWERTY keyboard typewriter did not include keys for the en dash and the em dash. To overcome this limitation, users typically typed more than one adjacent hyphen to approximate these symbols. This typewriter convention is still sometimes used today, even though modern computer word processing applications can input the correct en and em dashes for each font type. | Typewriter | Wikipedia | 467 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Other examples of typewriter practices that are sometimes still used in desktop publishing systems include inserting a double space between sentences, and the use of the typewriter apostrophe, , and straight quotes, , as quotation marks and prime marks. The practice of underlining text in place of italics and the use of all capitals to provide emphasis are additional examples of typographical conventions that derived from the limitations of the typewriter keyboard that still carry on today.
Many older typewriters did not include a separate key for the numeral or the exclamation point , and some even older ones also lacked the numeral zero, . Typists who trained on these machines learned the habit of using the lowercase letter ("ell") for the digit , and the uppercase ("oh") for the zero. A cents symbol, was created by combining (over-striking) a lower case with a slash character (typing , then backspace, then ). Similarly, the exclamation point was created by combining an apostrophe and a period ( ≈).
Terminology repurposed for the computer age
Some terminology from the typewriter age has survived into the computer era. | Typewriter | Wikipedia | 246 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
backspace (BS) – a keystroke that moved the cursor backwards one position (on a typewriter, this moved the physical platen backwards), to enable a character to be overtyped. Originally this was used to combine characters (for example, the sequence , backspace, to make ). Subsequently it facilitated "erase and retype" corrections (using correction tape or fluid.) Only the latter concept has survived into the computer age.
carriage return (CR) – return to the first column of text. (Most typewriters switched automatically to the next line. In computer systems, "line feed" (see below) is a function that is controlled independently.)
cursor – a marker used to indicate where the next character will be printed. The cursor was originally a term to describe the clear slider on a slide rule; on typewriters, it was the paper that moved and the insertion point was fixed.
cut and paste – taking text, a numerical table, or an image and pasting it into a document. The term originated when such compound documents were created using manual paste up techniques for typographic page layout. Actual brushes and paste were later replaced by hot-wax machines equipped with cylinders that applied melted adhesive wax to developed prints of "typeset" copy. This copy was then cut out with knives and rulers, and slid into position on layout sheets on slanting layout tables. After the "copy" had been correctly positioned and squared up using a T-square and set square, it was pressed down with a brayer, or roller. The whole point of the exercise was to create so-called "camera-ready copy" which existed only to be photographed and then printed, usually by offset lithography.
dead key – a key that, when typed, does not advance the typing position, thus allowing another character to be overstruck on top of the original character. This was typically used to combine diacritical marks with letters they modified (e.g. è can be generated by first pressing and then ). In Europe, where most languages have diacritics, a typical mechanical arrangement meant that hitting the accent key typed the symbol but did not advance the carriage, consequently the next character to be typed 'landed' on the same position. It was this method that carried across to the computer age whereas an alternative method (press the space bar simultaneously) did not. | Typewriter | Wikipedia | 496 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
line feed (LF), also called "newline" – Whereas most typewriters rolled the paper forward automatically on a "carriage return), this is an explicit control character on computer systems that moves the cursor to the next on-screen line of text. (But not to the beginning of that line a CR is also needed if that effect is desired.)
shift – a modifier key used to type capital letters and other alternate "upper case" characters; when pressed and held down, would shift a typewriter's mechanism to allow a different typebar impression (such as 'D' instead of 'd') to press into the ribbon and print on a page. The concept of a shift key or modifier key was later extended to Ctrl, Alt, AltGr and Super ("Windows" or "Apple") keys on modern computer keyboards. The generalized concept of a shift key reached its apex in the MIT space-cadet keyboard.
tab (HT), shortened from "horizontal tab" or "tabulator stop" – caused the print position to advance horizontally to the next pre-set "tab stop". This was used for typing lists and tables with vertical columns of numbers or words.
The vertical tab (VT) control character, named by analogy with HT, was designed for use with early computer line printers, and would cause the fan-fold paper to be fed until the next line's position.
tty, short for teletypewriter – used in Unix-like operating systems to designate a given "terminal". | Typewriter | Wikipedia | 320 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Social effects
When Remington started marketing typewriters, the company assumed the machine would not be used for composing but for transcribing dictation, and that the person typing would be a woman. The 1800s Sholes and Glidden typewriter had floral ornamentation on the case.
During World Wars I and II, increasing numbers of women were entering the workforce. In the United States, women often started in the professional workplace as copy typists. Being a typist was considered the right choice for a "good girl", meaning women who present themselves as being chaste and having good conduct. According to the 1900 census, 94.9% of stenographers and typists were unmarried women. This also led to an increase in schools and classes for typing in order to prepare for a future job. Moreover, the word "typewriter" also became associated with the women who typed during the timeperiod.
Questions about morals made a salacious businessman making sexual advances to a female typist into a cliché of office life, appearing in vaudeville and movies. The "Tijuana bibles" – adult comic books produced in Mexico for the American market, starting in the 1930s – often featured women typists. In one panel, a businessman in a three-piece suit, ogling his secretary's thigh, says, "Miss Higby, are you ready for—ahem!—er—dictation?"
The typewriter was a useful machine during the censorship era of the Soviet government, starting during the Russian Civil War (1917–1922). Samizdat was a form of surreptitious self-publication used when the government was censoring what literature the public could see. The Soviet government signed a Decree on Press which prohibited the publishing of any written work that had not been previously officially reviewed and approved. Unapproved work was copied manually, most often on typewriters. In 1983, a new law required anyone who needed a typewriter to get police permission to buy or keep one. In addition, the owner would have to register a typed sample of all its letters and numbers, to ensure that any illegal literature typed with it could be traced back to its source. The typewriter became increasingly popular as the interest in prohibited books grew.
Writers with notable associations with typewriters | Typewriter | Wikipedia | 480 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Early adopters
Henry James dictated to a typist.
Mark Twain claimed in his autobiography that he was the first important writer to present a publisher with a typewritten manuscript, for The Adventures of Tom Sawyer (1876). Research showed that Twain's memory was incorrect and that the first book submitted in typed form was Life on the Mississippi (1883, also by Twain).
Others
William S. Burroughs wrote in some of his novels – and possibly believed – that "a machine he called the 'Soft Typewriter' was writing our lives, and our books, into existence", according to a book review in The New Yorker. In the 1991 film adaptation of his 1959 novel Naked Lunch, his typewriter is a living, insect-like entity (voiced by North American actor Peter Boretski) and actually dictates the book to him.
J. R. R. Tolkien was accustomed to typing from awkward positions: "balancing his typewriter on his attic bed, because there was no room on his desk".
Jack Kerouac, a fast typist at 100 words per minute, typed his 1957 novel On the Road on a roll of paper so he would not be interrupted by having to change the paper. Within two weeks of starting to write On the Road, Kerouac had one single-spaced paragraph, long. Some scholars say the scroll was shelf paper; others contend it was a Thermal-fax roll; another theory is that the roll consisted of sheets of architect's paper taped together. Kerouac himself stated that he used rolls of teletype paper.
Don Marquis purposely used the limitations of a typewriter (or more precisely, a particular typist) in his archy and mehitabel series of newspaper columns, which were later compiled into a series of books. According to his literary conceit, a cockroach named "Archy" was a reincarnated free-verse poet, who would type articles overnight by jumping onto the keys of a manual typewriter. The writings were typed completely in lower case, because of the cockroach's inability to generate the heavy force needed to operate the shift key. The lone exception is the poem "CAPITALS AT LAST" from archys life of mehitabel, written in 1933.
Late users | Typewriter | Wikipedia | 465 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Richard Polt, a philosophy professor at Xavier University in Cincinnati who collects typewriters, has edited ETCetera, a quarterly magazine about historic writing machines, and is the author of the book The Typewriter Revolution: A Typist's Companion for the 21st Century.
William Gibson used a Hermes 2000 model manual typewriter to write his 1984 novel Neuromancer and half of Count Zero (1983) before a mechanical failure and lack of replacement parts forced him to upgrade to an Apple IIc computer.
Harlan Ellison used typewriters for his entire career, and when he was no longer able to have them repaired, learned to do it himself; he repeatedly stated his belief that computers are bad for writing, maintaining that "Art is not supposed to be easier!"
Cormac McCarthy wrote his novels on an Olivetti Lettera 32 typewriter until his death. In 2009, the Lettera he obtained from a pawn shop in 1963, on which nearly all his novels and screenplays were written, was auctioned for charity at Christie's for US$254,500; McCarthy obtained an identical replacement for $20 to continue writing on.
Will Self explains why he uses a manual typewriter: "I think the computer user does their thinking on the screen, and the non-computer user is compelled, because he or she has to retype a whole text, to do a lot more thinking in the head."
Ted Kaczynski (the "Unabomber") infamously used two old manual typewriters to write his polemic essays and messages.
Actor Tom Hanks uses and collects manual typewriters. To control the size of his collection, he gifts autographed machines to appreciative fans and repair shops around the world.
Historian David McCullough used a Royal typewriter to compose his books.
Biographer Robert Caro has used various models of the Smith Corona Electra 210 to write his biographies of Robert Moses and Lyndon Johnson.
Typewriters in popular culture
In music | Typewriter | Wikipedia | 407 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Erik Satie's 1917 score for the ballet Parade includes a "Mach. à écrire" as a percussion instrument, along with (elsewhere) a roulette wheel and a pistol.
The composer Leroy Anderson wrote The Typewriter (1950) for orchestra and typewriter, and it has since been used as the theme for numerous radio programs. The solo instrument is a real typewriter played by a percussionist. The piece was later made famous by comedian Jerry Lewis as part of his regular routine both on screen and stage, most notably in the 1963 film Who's Minding the Store?.
A typewriter plays an integral part (and is used on stage as a prop) in the song 'Opening Doors', from Stephen Sondheim's musical Merrily We Roll Along (1981).
Wordy Rappinghood, a 1981 single by Tom Tom Club, opens with the sound of a typewriter.
Typewriter samples are woven into the texture of 'Dissidents', the opening track of Thomas Dolby's 1984 album The Flat Earth.
The Boston Typewriter Orchestra (BTO), a comedic musical percussion group, has performed at numerous art festivals, clubs, and parties since 2004.
Max Richter's The Blue Notebooks (2004) features the sound of the typewriter underneath the narration of Tilda Swinton.
South Korean improviser Ryu Hankil frequently performs on typewriters, most prominently in his 2009 album Becoming Typewriter.
Other
The 2012 French comedy movie Populaire, starring Romain Duris and Déborah François, centers on a young secretary in the 1950s striving to win typewriting speed competitions.
The manga (2015–2020) and anime (2018) Violet Evergarden series follows a disabled war veteran who learns to type because her handwriting has been impaired, and soon she becomes a popular typist.
California Typewriter, a 2016 documentary film, investigates the culture of typewriter enthusiasts, including an eponymous repair store in Berkeley, California.
Forensic examination
Typewritten documents may be examined by forensic document examiners. This is done primarily to determine 1) the make and/or model of the typewriter used to produce a document, or 2) whether or not a particular suspect typewriter might have been used to produce a document. | Typewriter | Wikipedia | 464 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
The determination of a make and/or model of typewriter is a 'classification' problem and several systems have been developed for this purpose. These include the original Haas Typewriter Atlases (Pica version) and (Non-Pica version) and the TYPE system developed by Philip Bouffard, the Royal Canadian Mounted Police's Termatrex Typewriter classification system, and Interpol's typewriter classification system, among others.
The earliest reference in fictional literature to the potential identification of a typewriter as having produced a document was by Sir Arthur Conan Doyle, who wrote the Sherlock Holmes short story "A Case of Identity" in 1891.
In non-fiction, the first document examiner to describe how a typewriter might be identified was William E. Hagan who wrote, in 1894, "All typewriter machines, even when using the same kind of type, become more or less peculiar by use as to the work done by them". Other early discussions of the topic were provided by A. S. Osborn in his 1908 treatise, Typewriting as Evidence, and again in his 1929 textbook, Questioned Documents.
A modern description of the examination procedure is laid out in ASTM Standard E2494-08 (Standard Guide for Examination of Typewritten Items).
Typewriter examination was used in the Leopold and Loeb and Alger Hiss cases.
In the Eastern Bloc, typewriters (together with printing presses, copy machines, and later computer printers) were a controlled technology, with secret police in charge of maintaining records of the typewriters and their owners. In the Soviet Union, the First Department of each organization sent data on organization's typewriters to the KGB. This posed a significant risk for dissidents and samizdat authors. In Romania, according to State Council Decree No. 98 of March 28, 1983, owning a typewriter, both by businesses or by private persons, was subject to an approval given by the local police authorities. People previously convicted of any crime or those who because of their behaviour were considered to be "a danger to public order or to the security of the state" were refused approval. In addition, once a year, typewriter owners had to take the typewriter to the local police station, where they would be asked to type a sample of all the typewriter's characters. It was also forbidden to borrow, lend, or repair typewriters other than at the places that had been authorized by the police. | Typewriter | Wikipedia | 503 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Collections
Public and private collections of typewriters exist around the world, including:
Schreibmaschinenmuseum Peter Mitterhofer (Parcines, Italy)
Museo della Macchina da Scrivere (Milan, Italy)
Liverpool Typewriter Museum (Liverpool, England)
Museum of Printing – MoP (Haverhill, Massachusetts, US)
Chestnut Ridge Typewriter Museum (Fairmont, West Virginia, US)
Technical Museum of the Empordà (Figueres, Girona, Spain)
Musée de la machine à écrire (Lausanne, Switzerland)
Lu Hanbin Typewriter Museum Shanghai (Shanghai, China)
Wattens Typewriter Museum (Wattens, Austria)
German Typewriter Museum (Bayreuth, Germany)
Tayfun Talipoğlu Typewriter Museum (Odunpazarı, Eskişehir, Turkey)
Several online-only virtual museums collect and display information about typewriters and their history:
Virtual Typewriter Museum
Chuck & Rich's Antique Typewriter Website
Mr. Martin's Typewriter Museum
Gallery | Typewriter | Wikipedia | 215 | 44365 | https://en.wikipedia.org/wiki/Typewriter | Technology | Media and communication | null |
Triton is the largest natural satellite of the planet Neptune. It is the only moon of Neptune massive enough to be rounded under its own gravity and hosts a thin, hazy atmosphere. Triton orbits Neptune in a retrograde orbit—revolving in the opposite direction to the parent planet's rotation—the only large moon in the Solar System to do so. Triton is thought to have once been a dwarf planet from the Kuiper belt, captured into Neptune's orbit by the latter's gravity.
At in diameter, Triton is the seventh-largest moon in the Solar System, the second-largest planetary moon in relation to its primary (after Earth's Moon), and larger than all of the known dwarf planets. The mean density is , reflecting a composition of approximately 30–45% water ice by mass, with the rest being mostly rock and metal. Triton is differentiated, with a crust of primarily ice atop a probable subsurface ocean of liquid water and a solid rocky-metallic core at its center. Although Triton's orbit is nearly circular with a very low orbital eccentricity of , Triton's interior may still experience tidal heating through obliquity tides.
Triton is one of the most geologically active worlds in the Solar System, with an estimated average surface age of less than 100 million years old. Its surface is covered by frozen nitrogen and is geologically young, with very few impact craters. Young, intricate cryovolcanic and tectonic terrains suggest a complex geological history. The atmosphere of Triton is composed primarily of nitrogen, with minor components of methane and carbon monoxide. Triton's atmosphere is relatively thin and strongly variable, with its atmospheric surface pressure varying by up to a factor of three within the past 30 years. Triton's atmosphere supports clouds of nitrogen ice crystals and a layer of organic atmospheric haze.
Triton was the first Neptunian moon to be discovered, on October 10, 1846, by English astronomer William Lassell. The 1989 flyby of Triton by the Voyager 2 spacecraft remains the only up-close visit to the moon as of 2025. As the probe was only able to study about 40% of the moon's surface, multiple concept missions have been developed to revisit Triton. These include a Discovery-class Trident and New Frontiers-class Triton Ocean Worlds Surveyor and Nautilus.
Discovery and naming | Triton (moon) | Wikipedia | 493 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
Triton was discovered by British astronomer William Lassell on October 10, 1846, just 17 days after the discovery of Neptune. When John Herschel received news of Neptune's discovery, he wrote to Lassell suggesting he search for possible moons. Lassell discovered Triton eight days later. Lassell also claimed for a period to have discovered rings. Although Neptune was later confirmed to have rings, they are so faint and dark that it is not plausible he saw them. A brewer by trade, Lassell spotted Triton with his self-built aperture metal mirror reflecting telescope (also known as the "two-foot" reflector). This telescope was donated to the Royal Observatory, Greenwich in the 1880s, but was eventually dismantled.
Triton is named after the Greek sea god Triton (Τρίτων), the son of Poseidon (the Greek god corresponding to the Roman Neptune). The name was first proposed by Camille Flammarion in his 1880 book Astronomie Populaire, and was officially adopted many decades later. Until the discovery of the second moon Nereid in 1949, Triton was commonly referred to as "the satellite of Neptune". Lassell did not name his discovery; he later successfully suggested the name Hyperion for the eighth moon of Saturn when he discovered it.
Orbit and rotation
Triton is unique among all large moons in the Solar System for its retrograde orbit around its planet (i.e. it orbits in a direction opposite to the planet's rotation). Most of the outer irregular moons of Jupiter and Saturn also have retrograde orbits, as do some of the irregular moons of Uranus and Neptune. However, these moons are all much more distant from their primaries and are small in comparison with the largest of them (Phoebe) having only 8% of the diameter (and 0.03% of the mass) of Triton. | Triton (moon) | Wikipedia | 384 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
Triton's orbit is associated with two tilts, the obliquity of Neptune's rotation to Neptune's orbit, 30°, and the inclination of Triton's orbit to Neptune's rotation, 157° (an inclination over 90° indicates retrograde motion). Triton's orbit precesses forward relative to Neptune's rotation with a period of about 678 Earth years (4.1 Neptunian years), making its Neptune-orbit-relative inclination vary between 127° and 173°. That inclination is currently 130°; Triton's orbit is now near its maximum departure from coplanarity with Neptune's.
Triton's rotation is tidally locked to be synchronous with its orbit around Neptune: it keeps one face oriented toward the planet at all times. Its equator is almost exactly aligned with its orbital plane. At present, Triton's rotational axis is about 40° from Neptune's orbital plane, hence as Neptune orbits the Sun, Triton's polar regions take turns facing the Sun, resulting in seasonal changes as one pole, then the other moves into the sunlight. Such changes were observed in 2010.
Triton's revolution around Neptune has become a nearly perfect circle with an eccentricity of almost zero. Viscoelastic damping from tides alone is not thought to be capable of circularizing Triton's orbit in the time since the origin of the system, and gas drag from a prograde debris disc is likely to have played a substantial role. Tidal interactions also cause Triton's orbit, which is already closer to Neptune than the Moon is to Earth, to gradually decay further; predictions are that 3.6 billion years from now, Triton will pass within Neptune's Roche limit. This will result in either a collision with Neptune's atmosphere or the breakup of Triton, forming a new ring system similar to that found around Saturn.
Capture | Triton (moon) | Wikipedia | 397 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
The current understanding of moons in retrograde orbits means they cannot form in the same region of the solar nebula as the planets they orbit. Therefore Triton must have been captured from elsewhere in the Solar System. Astrophysicists believe it might have originated in the Kuiper belt, a ring of small icy objects extending from just inside the orbit of Neptune to about 50 AU from the Sun. Thought to be the point of origin for the majority of short-period comets observed from Earth, the belt is also home to several large, planet-like bodies including Pluto, which is now recognized as the largest in a population of Kuiper belt objects (the plutinos) locked in resonant orbits with Neptune. Triton is only slightly larger than Pluto and is nearly identical in composition, which has led to the hypothesis that the two share a common origin.
This has been further supported in a 2024 study of the chemical composition of Pluto and Triton which suggests they originated in the same region of the outer Solar System before the latter was pulled into Neptune’s orbit. Kathleen Mandt at NASA's Goddard Space Flight Center in Maryland and her colleagues hypothesize that Triton and Pluto formed close to each other before the Solar System settled down. "They probably formed in the same region, which wouldn't be where the Kuiper belt is now—it would have been either closer or further away," says Mandt.
Studying prior data on the two bodies, the team found that both have a large amount of nitrogen and trace amounts of methane and carbon monoxide, which could have accumulated in the outer regions of the young nebula "For some reason, Triton was then ejected from this region and ensnared by Neptune". "They had to have formed beyond the water-ice line," says Mandt, referring to the distance from the sun where water would freeze into ice or snow, which is why Triton and Pluto have similar amounts of certain key elements. "One possibility is that the giant planets moved closer to the sun early in the first 100 million years or so of the Solar System, which may have disrupted the orbits of some bodies like Triton.", says Mandt. | Triton (moon) | Wikipedia | 451 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
The proposed capture of Triton may explain several features of the Neptunian system, including the extremely eccentric orbit of Neptune's moon Nereid and the scarcity of moons as compared to the other giant planets. Triton's initially eccentric orbit would have intersected the orbits of irregular moons and disrupted those of smaller regular moons, dispersing them through gravitational interactions.
Triton's eccentric post-capture orbit would have also resulted in tidal heating of its interior, which could have kept Triton fluid for a billion years; this inference is supported by evidence of differentiation in Triton's interior. This source of internal heat disappeared following tidal locking and circularization of the orbit.
Two types of mechanisms have been proposed for Triton's capture. To be gravitationally captured by a planet, a passing body must lose sufficient energy to be slowed down to a speed less than that required to escape. An early model of how Triton may have been slowed was by collision with another object, either one that happened to be passing by Neptune (which is unlikely), or a moon or proto-moon in orbit around Neptune (which is more likely). A more recent hypothesis suggests that, before its capture, Triton was part of a binary system. When this binary encountered Neptune, it interacted in such a way that the binary dissociated, with one portion of the binary expelled, and the other, Triton, becoming bound to Neptune. This event is more likely for more massive companions. This hypothesis is supported by several lines of evidence, including binaries being very common among the large Kuiper belt objects. The event was brief but gentle, saving Triton from collisional disruption. Events like this may have been common during the formation of Neptune, or later when it migrated outward.
However, simulations in 2017 showed that after Triton's capture, and before its orbital eccentricity decreased, it probably did collide with at least one other moon, and caused collisions between other moons.
Physical characteristics | Triton (moon) | Wikipedia | 409 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
Triton is the seventh-largest moon and sixteenth-largest object in the Solar System and is modestly larger than the dwarf planets Pluto and Eris. It is also the largest retrograde moon in the Solar System. It accounts for more than 99.5% of all the mass known to orbit Neptune, including the planet's rings and fifteen other known moons, and is also more massive than all known moons in the Solar System smaller than itself combined. Also, with a diameter 5.5% that of Neptune, it is the largest moon of a gas giant relative to its planet in terms of diameter, although Titan is bigger relative to Saturn in terms of mass (the ratio of Triton's mass to that of Neptune is approximately 1:4788). It has a radius, density (2.061 g/cm3), temperature and chemical composition similar to that of Pluto.
Triton's surface is covered with a transparent layer of annealed frozen nitrogen. Only 40% of Triton's surface has been observed and studied, but it may be entirely covered in such a thin sheet of nitrogen ice. Triton's surface consists of 55% nitrogen ice with other ices mixed in. Water ice comprises 15–35% and frozen carbon dioxide (dry ice) the remaining 10–20%. Trace ices include 0.1% methane and 0.05% carbon monoxide. There could also be ammonia ice on the surface, as there are indications of ammonia dihydrate in the lithosphere. Triton's mean density implies that it probably consists of about 30–45% water ice (including relatively small amounts of volatile ices), with the remainder being rocky material. Triton's surface area is 23 million km2, which is 4.5% of Earth, or 15.5% of Earth's land area. Triton has an unusually high albedo, reflecting 60–95% of the sunlight that reaches it, and it has changed only slightly since the first observations. By comparison, the Moon reflects only 11%. This high albedo causes Triton to reflect a lot of whatever little sunlight there is instead of absorbing it, causing it to have the coldest recorded temperature in the Solar System at . Triton's reddish color is thought to be the result of methane ice, which is converted to tholins under exposure to ultraviolet radiation. | Triton (moon) | Wikipedia | 493 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
Because Triton's surface indicates a long history of melting, models of its interior posit that Triton is differentiated, like Earth, into a solid core, a mantle and a crust. Water, the most abundant volatile in the Solar System, comprises Triton's mantle, enveloping a core of rock and metal. There is enough rock in Triton's interior for radioactive decay to maintain a liquid subsurface ocean to this day, similar to what is thought to exist beneath the surface of Europa and several other icy outer Solar System worlds. This is not thought to be adequate to power convection in Triton's icy crust. However, the strong obliquity tides are believed to generate enough additional heat to accomplish this and produce the observed signs of recent surface geological activity. The black material ejected is suspected to contain organic compounds, and if liquid water is present on Triton, it has been speculated that this could make it habitable for some form of life.
Atmosphere
Triton has a tenuous but well-structured and global nitrogen atmosphere, with trace amounts of carbon monoxide and small amounts of methane near its surface. Like Pluto's atmosphere, the atmosphere of Triton is thought to result from the evaporation of nitrogen from its surface. Its surface temperature is at least because Triton's nitrogen ice is in the warmer, hexagonal crystalline state, and the phase transition between hexagonal and cubic nitrogen ice occurs at that temperature. An upper limit in the low 40s (K) can be set from vapor pressure equilibrium with nitrogen gas in Triton's atmosphere. This is colder than Pluto's average equilibrium temperature of . Triton's surface atmospheric pressure is only about . | Triton (moon) | Wikipedia | 349 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
Turbulence at Triton's surface creates a troposphere (a "weather region") rising to an altitude of 8 km. Streaks on Triton's surface left by geyser plumes suggest that the troposphere is driven by seasonal winds capable of moving material over a micrometer in size. Unlike other atmospheres, Triton's lacks a stratosphere and instead has a thermosphere from altitudes of 8 to 950 km and an exosphere above that. The temperature of Triton's upper atmosphere, at , is higher than that at its surface, due to heat absorbed from solar radiation and Neptune's magnetosphere. A haze permeates most of Triton's troposphere, thought to be composed largely of hydrocarbons and nitriles created by the action of sunlight on methane. Triton's atmosphere also has clouds of condensed nitrogen that lie between 1 and 3 km from its surface.
In 1997, observations from Earth were made of Triton's limb as it passed in front of stars. These observations indicated the presence of a denser atmosphere than was deduced from Voyager 2 data. Other observations have shown an increase in temperature by 5% from 1989 to 1998. These observations indicated Triton was approaching an unusually warm southern hemisphere summer season that happens only once every few hundred years. Hypotheses for this warming include a change of frost patterns on Triton's surface and a change in ice albedo, which would allow more heat to be absorbed. Another hypothesis argues that temperature changes are a result of the deposition of dark, red material from geological processes. Because Triton's Bond albedo is among the highest in the Solar System, it is sensitive to small variations in spectral albedo. Based on the increase in atmospheric pressure between 1989 and 1997, it is estimated that by 2010 Triton's atmospheric pressure may have increased to as much as 4 Pa. By 2017, however, Triton's atmospheric surface pressure had nearly returned to Voyager 2 levels; the cause for the rapid spike in atmospheric pressure between 1989 and 2017 remains unexplained.
Surface features | Triton (moon) | Wikipedia | 432 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
All detailed knowledge of the surface of Triton was acquired from a distance of 40,000 km by the Voyager 2 spacecraft during a single encounter in 1989. The 40% of Triton's surface imaged by Voyager 2 revealed blocky outcrops, ridges, troughs, furrows, hollows, plateaus, icy plains and a few craters. Triton is relatively flat; its observed topography never varies beyond a kilometer. The impact craters observed are concentrated almost entirely in Triton's leading hemisphere. Analysis of crater density and distribution has suggested that in geological terms, Triton's surface is extremely young, with regions varying from an estimated 50 million years old to just an estimated 6 million years old. Fifty-five percent of Triton's surface is covered with frozen nitrogen, with water ice comprising 15–35% and frozen CO2 forming the remaining 10–20%. The surface also has deposits of tholins, a dark, tarry slurry of various organic chemical compounds.
Cryovolcanism
One of the largest cryovolcanic features found on Triton is Leviathan Patera, a caldera-like feature roughly 100 km in diameter seen near the equator. Surrounding this caldera is a massive cryovolcanic plain, Cipango Planum, which is at least 490,000 km2 in area; assuming Leviathan Patera is the primary vent, Leviathan Patera is one of the largest volcanic or cryovolcanic constructs in the Solar System. This feature is also connected to two enormous cryolava lakes seen northwest of the caldera. Because the cryolava on Triton is believed to be primarily water ice with some ammonia, these lakes would qualify as stable bodies of surface liquid water while they were molten. This is the first place such bodies have been found apart from Earth, and Triton is the only icy body known to feature cryolava lakes, although similar cryomagmatic extrusions can be seen on Ariel, Ganymede, Charon, and Titan.
Plumes | Triton (moon) | Wikipedia | 422 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
The Voyager 2 probe in 1989 observed a handful of geyser-like eruptions of nitrogen gas or water and entrained dust from beneath the surface of Triton in plumes up to 8 km high. Triton is thus one of the few bodies in the Solar System on which active eruptions of some sort have been observed. The best-observed examples are the Hili plume and Mahilani plume (named after a Zulu water sprite and a Tongan sea spirit, respectively).
The precise mechanism behind Triton's plumes is debated; one hypothesis is that Triton's plumes are driven by solar heating underneath a transparent or translucent layer of nitrogen ice, creating a sort of "solid greenhouse effect". As solar radiation warms the darker material beneath, this causes a rapid increase in pressure as the nitrogen begins to sublimate until enough pressure accumulates for it to erupt through the translucent layer. This model is largely supported by the observation that Triton was near peak southern summer at the time of Voyager 2s flyby, ensuring its southern polar cap was receiving prolonged sunlight. If this were the case, CO2 geysers on Mars are thought to erupt from its south polar cap each spring in the same way.
However, the significant geological activity on Triton has led to alternative proposals that the plumes may be cryovolcanic in nature, rather than driven by solar radiation. A cryovolcanic origin better explains the estimated output of Triton’s plumes, which possibly exceeds . This is similar to that which is estimated for Enceladus's cryovolcanic plumes at . However, if Triton's plumes are cryovolcanically driven, it remains to be explained why they predominantly appear over its southern polar cap. Triton's high surface heat flux may directly melt or vaporize nitrogen ice at the base of its polar caps, creating 'hot spots' which break through the ice or move to the ice caps' margins, before erupting explosively.
Though only observed up close once by the Voyager 2 spacecraft, it is estimated that a plume eruption on Triton may last up to a year.
Polar cap, plains and ridges | Triton (moon) | Wikipedia | 454 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
Triton's south polar region is covered by a highly reflective cap of frozen nitrogen and methane sprinkled by impact craters and openings of geysers. Little is known about the north pole because it was on the night side during the Voyager 2 encounter, but it is thought that Triton must also have a north polar ice cap.
The high plains found on Triton's eastern hemisphere, such as Cipango Planum, cover over and blot out older features, and are therefore almost certainly the result of icy lava washing over the previous landscape. The plains are dotted with pits, such as Leviathan Patera, which are probably the vents from which this lava emerged. The composition of the lava is unknown, although a mixture of ammonia and water is suspected.
Four roughly circular "walled plains" have been identified on Triton. They are the flattest regions so far discovered, with a variance in altitude of less than 200 m. They are thought to have formed from the eruption of icy lava. The plains near Triton's eastern limb are dotted with black spots, the maculae. Some maculae are simple dark spots with diffuse boundaries, and others comprise a dark central patch surrounded by a white halo with sharp boundaries. The maculae typically have diameters of about 100 km and widths of the halos of between 20 and 30 km.
There are extensive ridges and valleys in complex patterns across Triton's surface, probably the result of freeze–thaw cycles. Many also appear to be tectonic and may result from an extension or strike-slip faulting. There are long double ridges of ice with central troughs bearing a strong resemblance to Europan lineae (although they have a larger scale), and which may have a similar origin, possibly shear heating from strike-slip motion along faults caused by diurnal tidal stresses experienced before Triton's orbit was fully circularized. These faults with parallel ridges expelled from the interior cross complex terrain with valleys in the equatorial region. The ridges and furrows, or sulci, such as Yasu Sulci, Ho Sulci, and Lo Sulci, are thought to be of intermediate age in Triton's geological history, and in many cases to have formed concurrently. They tend to be clustered in groups or "packets".
Cantaloupe terrain | Triton (moon) | Wikipedia | 478 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
Triton's western hemisphere consists of a strange series of fissures and depressions known as "cantaloupe terrain" because it resembles the skin of a cantaloupe melon. Although it has few craters, it is thought that this is the oldest terrain on Triton. It probably covers much of Triton's western half.
Cantaloupe terrain, which is mostly dirty water ice, is only known to exist on Triton. It contains depressions in diameter. The depressions (cavi) are probably not impact craters because they are all of the similar size and have smooth curves. The leading hypothesis for their formation is diapirism, the rising of "lumps" of less dense material through a stratum of denser material. Alternative hypotheses include formation by collapses, or by flooding caused by cryovolcanism.
Impact craters
Due to constant erasure and modification by ongoing geological activity, impact craters on Triton's surface are relatively rare. A census of Triton's craters imaged by Voyager 2 found only 179 that were incontestably of impact origin, compared with 835 observed for Uranus's moon Miranda, which has only three percent of Triton's surface area. The largest crater observed on Triton thought to have been created by an impact is a feature called Mazomba. Although larger craters have been observed, they are generally thought to be volcanic.
The few impact craters on Triton are almost all concentrated in the leading hemisphere—that facing the direction of the orbital motion—with the majority concentrated around the equator between 30° and 70° longitude, resulting from material swept up from orbit around Neptune. Because it orbits with one side permanently facing the planet, astronomers expect that Triton should have fewer impacts on its trailing hemisphere, due to impacts on the leading hemisphere being more frequent and more violent. Voyager 2 imaged only 40% of Triton's surface, so this remains uncertain. However, the observed cratering asymmetry exceeds what can be explained based on the impactor populations, and implies a younger surface age for the crater-free regions (≤ 6 million years old) than for the cratered regions (≤ 50 million years old).
Observation and exploration | Triton (moon) | Wikipedia | 461 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
The orbital properties of Triton were already determined with high accuracy in the 19th century. It was found to have a retrograde orbit, at a very high angle of inclination to the plane of Neptune's orbit. The first detailed observations of Triton were not made until 1930. Little was known about the satellite until Voyager 2 flew by in 1989.
Before the flyby of Voyager 2, astronomers suspected that Triton might have liquid nitrogen seas and a nitrogen/methane atmosphere with a density as much as 30% that of Earth. Like the famous overestimates of the atmospheric density of Mars, this proved incorrect. As with Mars, a denser atmosphere is postulated for its early history.
The first attempt to measure the diameter of Triton was made by Gerard Kuiper in 1954. He obtained a value of 3,800 km. Subsequent measurement attempts arrived at values ranging from 2,500 to 6,000 km, or from slightly smaller than the Moon (3,474.2 km) to nearly half the diameter of Earth. Data from the approach of Voyager 2 to Neptune on August 25, 1989, led to a more accurate estimate of Triton's diameter (2,706 km).
In the 1990s, various observations from Earth were made of the limb of Triton using the occultation of nearby stars, which indicated the presence of an atmosphere and an exotic surface. Observations in late 1997 suggest that Triton is heating up and the atmosphere has become significantly denser since Voyager 2 flew past in 1989. | Triton (moon) | Wikipedia | 309 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
New concepts for missions to the Neptune system to be conducted in the 2010s were proposed by NASA scientists on numerous occasions over the last decades. All of them identified Triton as being a prime target and a separate Triton lander comparable to the Huygens probe for Titan was frequently included in those plans. No efforts aimed at Neptune and Triton went beyond the proposal phase and NASA's funding for missions to the outer Solar System is currently focused on the Jupiter and Saturn systems. A proposed lander mission to Triton, called Triton Hopper, would mine nitrogen ice from the surface of Triton and process it to be used as a propellant for a small rocket, enabling it to fly or 'hop' across the surface. Another concept, involving a flyby, was formally proposed in 2019 as part of NASA's Discovery Program under the name Trident. Neptune Odyssey is a mission concept for a Neptune orbiter with a focus on Triton being studied beginning April 2021 as a possible large strategic science mission by NASA that would launch in 2033 and arrive at the Neptune system in 2049. Two lower-cost mission concepts were subsequently developed for the New Frontiers program: the first the following June and the second in 2023. The first is Triton Ocean World Surveyor, which would launch in 2031 and arrive in 2047, and the second is Nautilus, which would launch August 2042 and arrive in April 2057.
Maps | Triton (moon) | Wikipedia | 290 | 44371 | https://en.wikipedia.org/wiki/Triton%20%28moon%29 | Physical sciences | Solar System | null |
Brown dwarfs are substellar objects that have more mass than the biggest gas giant planets, but less than the least massive main-sequence stars. Their mass is approximately 13 to 80 times that of Jupiter ()not big enough to sustain nuclear fusion of ordinary hydrogen (1H) into helium in their cores, but massive enough to emit some light and heat from the fusion of deuterium (2H). The most massive ones (> ) can fuse lithium (7Li).
Astronomers classify self-luminous objects by spectral type, a distinction intimately tied to the surface temperature, and brown dwarfs occupy types M, L, T, and Y. As brown dwarfs do not undergo stable hydrogen fusion, they cool down over time, progressively passing through later spectral types as they age.
Their name comes not from the color of light they emit but from their falling between white dwarf stars and "dark" planets in size. To the naked eye, brown dwarfs would appear in different colors depending on their temperature. The warmest ones are possibly orange or red, while cooler brown dwarfs would likely appear magenta or black to the human eye. Brown dwarfs may be fully convective, with no layers or chemical differentiation by depth.
Though their existence was initially theorized in the 1960s, it was not until the mid-1990s that the first unambiguous brown dwarfs were discovered. As brown dwarfs have relatively low surface temperatures, they are not very bright at visible wavelengths, emitting most of their light in the infrared. However, with the advent of more capable infrared detecting devices, thousands of brown dwarfs have been identified. The nearest known brown dwarfs are located in the Luhman 16 system, a binary of L- and T-type brown dwarfs about from the Sun. Luhman 16 is the third closest system to the Sun after Alpha Centauri and Barnard's Star.
History
Early theorizing | Brown dwarf | Wikipedia | 382 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
The objects now called "brown dwarfs" were theorized by Shiv S. Kumar in the 1960s to exist and were originally called black dwarfs, a classification for dark substellar objects floating freely in space that were not massive enough to sustain hydrogen fusion. However, (a) the term black dwarf was already in use to refer to a cold white dwarf; (b) red dwarfs fuse hydrogen; and (c) these objects may be luminous at visible wavelengths early in their lives. Because of this, alternative names for these objects were proposed, including and substar. In 1975, Jill Tarter suggested the term "brown dwarf", using "brown" as an approximate color.
The term "black dwarf" still refers to a white dwarf that has cooled to the point that it no longer emits significant amounts of light. However, the time required for even the lowest-mass white dwarf to cool to this temperature is calculated to be longer than the current age of the universe; hence such objects are expected to not yet exist.
Early theories concerning the nature of the lowest-mass stars and the hydrogen-burning limit suggested that a population I object with a mass less than 0.07 solar masses () or a population II object less than would never go through normal stellar evolution and would become a completely degenerate star. The resulting brown dwarf star is sometimes called a failed star. The first self-consistent calculation of the hydrogen-burning minimum mass confirmed a value between 0.07 and 0.08 solar masses for population I objects.
Deuterium fusion
The discovery of deuterium burning down to () and the impact of dust formation in the cool outer atmospheres of brown dwarfs in the late 1980s brought these theories into question. However, such objects were hard to find because they emit almost no visible light. Their strongest emissions are in the infrared (IR) spectrum, and ground-based IR detectors were too imprecise at that time to readily identify any brown dwarfs.
Since then, numerous searches by various methods have sought these objects. These methods included multi-color imaging surveys around field stars, imaging surveys for faint companions of main-sequence dwarfs and white dwarfs, surveys of young star clusters, and radial velocity monitoring for close companions. | Brown dwarf | Wikipedia | 451 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
GD 165B and class L
For many years, efforts to discover brown dwarfs were fruitless. In 1988, however, a faint companion to the white dwarf star GD 165 was found in an infrared search of white dwarfs. The spectrum of the companion GD 165B was very red and enigmatic, showing none of the features expected of a low-mass red dwarf. It became clear that GD 165B would need to be classified as a much cooler object than the latest M dwarfs then known. GD 165B remained unique for almost a decade until the advent of the Two Micron All-Sky Survey (2MASS) in 1997, which discovered many objects with similar colors and spectral features.
Today, GD 165B is recognized as the prototype of a class of objects now called "L dwarfs".
Although the discovery of the coolest dwarf was highly significant at the time, it was debated whether GD 165B would be classified as a brown dwarf or simply a very-low-mass star, because observationally it is very difficult to distinguish between the two.
Soon after the discovery of GD 165B, other brown-dwarf candidates were reported. Most failed to live up to their candidacy, however, because the absence of lithium showed them to be stellar objects. True stars burn their lithium within a little over 100 Myr, whereas brown dwarfs (which can, confusingly, have temperatures and luminosities similar to true stars) will not. Hence, the detection of lithium in the atmosphere of an object older than 100 Myr ensures that it is a brown dwarf.
Gliese 229B and class T
The first class "T" brown dwarf was discovered in 1994 by Caltech astronomers Shrinivas Kulkarni, Tadashi Nakajima, Keith Matthews and Rebecca Oppenheimer, and Johns Hopkins scientists Samuel T. Durrance and David Golimowski. It was confirmed in 1995 as a substellar companion to Gliese 229. Gliese 229b is one of the first two instances of clear evidence for a brown dwarf, along with Teide 1. Confirmed in 1995, both were identified by the presence of the 670.8 nm lithium line. The latter was found to have a temperature and luminosity well below the stellar range. | Brown dwarf | Wikipedia | 464 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
Its near-infrared spectrum clearly exhibited a methane absorption band at 2 micrometres, a feature that had previously only been observed in the atmospheres of giant planets and that of Saturn's moon Titan. Methane absorption is not expected at any temperature of a main-sequence star. This discovery helped to establish yet another spectral class even cooler than L dwarfs, known as "T dwarfs", for which Gliese 229B is the prototype.
Teide 1 and class M
The first confirmed class "M" brown dwarf was discovered by Spanish astrophysicists Rafael Rebolo (head of the team), María Rosa Zapatero-Osorio, and Eduardo L. Martín in 1994. This object, found in the Pleiades open cluster, received the name Teide 1. The discovery article was submitted to Nature in May 1995, and published on 14 September 1995. Nature highlighted "Brown dwarfs discovered, official" on the front page of that issue.
Teide 1 was discovered in images collected by the IAC team on 6 January 1994 using the 80 cm telescope (IAC 80) at Teide Observatory, and its spectrum was first recorded in December 1994 using the 4.2 m William Herschel Telescope at Roque de los Muchachos Observatory (La Palma). The distance, chemical composition, and age of Teide 1 could be established because of its membership in the young Pleiades star cluster. Using the most advanced stellar and substellar evolution models at that moment, the team estimated for Teide 1 a mass of , which is below the stellar-mass limit. The object became a reference in subsequent young brown dwarf related works.
In theory, a brown dwarf below is unable to burn lithium by thermonuclear fusion at any time during its evolution. This fact is one of the lithium test principles used to judge the substellar nature of low-luminosity and low-surface-temperature astronomical bodies.
High-quality spectral data acquired by the Keck 1 telescope in November 1995 showed that Teide 1 still had the initial lithium abundance of the original molecular cloud from which Pleiades stars formed, proving the lack of thermonuclear fusion in its core. These observations fully confirmed that Teide 1 is a brown dwarf, as well as the efficiency of the spectroscopic lithium test. | Brown dwarf | Wikipedia | 472 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
For some time, Teide 1 was the smallest known object outside the Solar System that had been identified by direct observation. Since then, over 1,800 brown dwarfs have been identified, even some very close to Earth, like Epsilon Indi Ba and Bb, a pair of brown dwarfs gravitationally bound to a Sun-like star 12 light-years from the Sun, and Luhman 16, a binary system of brown dwarfs at 6.5 light-years from the Sun.
Theory
The standard mechanism for star birth is through the gravitational collapse of a cold interstellar cloud of gas and dust. As the cloud contracts, it heats due to the Kelvin–Helmholtz mechanism. Early in the process the contracting gas quickly radiates away much of the energy, allowing the collapse to continue. Eventually, the central region becomes sufficiently dense to trap radiation. Consequently, the central temperature and density of the collapsed cloud increase dramatically with time, slowing the contraction, until the conditions are hot and dense enough for thermonuclear reactions to occur in the core of the protostar. For a typical star, gas and radiation pressure generated by the thermonuclear fusion reactions within its core will support it against any further gravitational contraction. Hydrostatic equilibrium is reached, and the star will spend most of its lifetime fusing hydrogen into helium as a main-sequence star.
If, however, the initial mass of the protostar is less than about , normal hydrogen thermonuclear fusion reactions will not ignite in the core. Gravitational contraction does not heat the small protostar very effectively, and before the temperature in the core can increase enough to trigger fusion, the density reaches the point where electrons become closely packed enough to create quantum electron degeneracy pressure. According to the brown dwarf interior models, typical conditions in the core for density, temperature and pressure are expected to be the following:
This means that the protostar is not massive or dense enough ever to reach the conditions needed to sustain hydrogen fusion. The infalling matter is prevented, by electron degeneracy pressure, from reaching the densities and pressures needed.
Further gravitational contraction is prevented and the result is a brown dwarf that simply cools off by radiating away its internal thermal energy. Note that, in principle, it is possible for a brown dwarf to slowly accrete mass above the hydrogen burning limit without initiating hydrogen fusion. This could happen via mass transfer in a binary brown dwarf system. | Brown dwarf | Wikipedia | 498 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
High-mass brown dwarfs versus low-mass stars
Lithium is generally present in brown dwarfs and not in low-mass stars. Stars, which reach the high temperature necessary for fusing hydrogen, rapidly deplete their lithium. Fusion of lithium-7 and a proton occurs, producing two helium-4 nuclei. The temperature necessary for this reaction is just below that necessary for hydrogen fusion. Convection in low-mass stars ensures that lithium in the whole volume of the star is eventually depleted. Therefore, the presence of the lithium spectral line in a candidate brown dwarf is a strong indicator that it is indeed a substellar object.
Lithium test
The use of lithium to distinguish candidate brown dwarfs from low-mass stars is commonly referred to as the lithium test, and was pioneered by Rafael Rebolo, Eduardo Martín and Antonio Magazzu. However, lithium is also seen in very young stars, which have not yet had enough time to burn it all.
Heavier stars, like the Sun, can also retain lithium in their outer layers, which never get hot enough to fuse lithium, and whose convective layer does not mix with the core where the lithium would be rapidly depleted. Those larger stars are easily distinguishable from brown dwarfs by their size and luminosity.
Conversely, brown dwarfs at the high end of their mass range can be hot enough to deplete their lithium when they are young. Dwarfs of mass greater than can burn their lithium by the time they are half a billion years old; thus the lithium test is not perfect.
Atmospheric methane
Unlike stars, older brown dwarfs are sometimes cool enough that, over very long periods of time, their atmospheres can gather observable quantities of methane, which cannot form in hotter objects. Dwarfs confirmed in this fashion include Gliese 229B.
Iron, silicate and sulfide clouds
Main-sequence stars cool, but eventually reach a minimum bolometric luminosity that they can sustain through steady fusion. This luminosity varies from star to star, but is generally at least 0.01% that of the Sun. Brown dwarfs cool and darken steadily over their lifetimes; sufficiently old brown dwarfs will be too faint to be detectable. | Brown dwarf | Wikipedia | 443 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
Clouds are used to explain the weakening of the iron hydride (FeH) spectral line in late L-dwarfs. Iron clouds deplete FeH in the upper atmosphere, and the cloud layer blocks the view to lower layers still containing FeH. The later strengthening of this chemical compound at cooler temperatures of mid- to late T-dwarfs is explained by disturbed clouds that allows a telescope to look into the deeper layers of the atmosphere that still contains FeH. Young L/T-dwarfs (L2-T4) show high variability, which could be explained with clouds, hot spots, magnetically driven aurorae or thermochemical instabilities. The clouds of these brown dwarfs are explained as either iron clouds with varying thickness or a lower thick iron cloud layer and an upper silicate cloud layer. This upper silicate cloud layer can consist out of quartz, enstatite, corundum and/or fosterite. It is however not clear if silicate clouds are always necessary for young objects. Silicate absorption can be directly observed in the mid-infrared at 8 to 12 μm. Observations with Spitzer IRS have shown that silicate absorption is common, but not ubiquitous, for L2-L8 dwarfs. Additionally, MIRI has observed silicate absorption in the planetary-mass companion VHS 1256b.
Iron rain as part of atmospheric convection processes is possible only in brown dwarfs, and not in small stars. The spectroscopy research into iron rain is still ongoing, but not all brown dwarfs will always have this atmospheric anomaly. In 2013, a heterogeneous iron-containing atmosphere was imaged around the B component in the nearby Luhman 16 system.
For late T-type brown dwarfs only a few variable searches were carried out. Thin cloud layers are predicted to form in late T-dwarfs from chromium and potassium chloride, as well as several sulfides. These sulfides are manganese sulfide, sodium sulfide and zinc sulfide. The variable T7 dwarf 2M0050–3322 is explained to have a top layer of potassium chloride clouds, a mid layer of sodium sulfide clouds and a lower layer of manganese sulfide clouds. Patchy clouds of the top two cloud layers could explain why the methane and water vapor bands are variable.
At the lowest temperatures of the Y-dwarf WISE 0855-0714 patchy cloud layers of sulfide and water ice clouds could cover 50% of the surface. | Brown dwarf | Wikipedia | 509 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
Low-mass brown dwarfs versus high-mass planets
Like stars, brown dwarfs form independently, but, unlike stars, they lack sufficient mass to "ignite" hydrogen fusion. Like all stars, they can occur singly or in close proximity to other stars. Some orbit stars and can, like planets, have eccentric orbits.
Size and fuel-burning ambiguities
Brown dwarfs are all roughly the same radius as Jupiter. At the high end of their mass range (), the volume of a brown dwarf is governed primarily by electron-degeneracy pressure, as it is in white dwarfs; at the low end of the range (), their volume is governed primarily by Coulomb pressure, as it is in planets. The net result is that the radii of brown dwarfs vary by only 10–15% over the range of possible masses. Moreover, the mass–radius relationship shows no change from about one Saturn mass to the onset of hydrogen burning (), suggesting that from this perspective brown dwarfs are simply high-mass Jovian planets. This can make distinguishing them from planets difficult.
In addition, many brown dwarfs undergo no fusion; even those at the high end of the mass range (over ) cool quickly enough that after 10 million years they no longer undergo fusion.
Heat spectrum
X-ray and infrared spectra are telltale signs of brown dwarfs. Some emit X-rays; and all "warm" dwarfs continue to glow tellingly in the red and infrared spectra until they cool to planet-like temperatures (under ).
Gas giants have some of the characteristics of brown dwarfs. Like the Sun, Jupiter and Saturn are both made primarily of hydrogen and helium. Saturn is nearly as large as Jupiter, despite having only 30% the mass. Three of the giant planets in the Solar System (Jupiter, Saturn, and Neptune) emit much more (up to about twice) heat than they receive from the Sun. All four giant planets have their own "planetary" systems, in the form of extensive moon systems.
Current IAU standard
Currently, the International Astronomical Union considers an object above (the limiting mass for thermonuclear fusion of deuterium) to be a brown dwarf, whereas an object under that mass (and orbiting a star or stellar remnant) is considered a planet. The minimum mass required to trigger sustained hydrogen burning (about ) forms the upper limit of the definition. | Brown dwarf | Wikipedia | 487 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
It is also debated whether brown dwarfs would be better defined by their formation process rather than by theoretical mass limits based on nuclear fusion reactions. Under this interpretation brown dwarfs are those objects that represent the lowest-mass products of the star formation process, while planets are objects formed in an accretion disk surrounding a star. The coolest free-floating objects discovered, such as WISE 0855, as well as the lowest-mass young objects known, like PSO J318.5−22, are thought to have masses below , and as a result are sometimes referred to as planetary-mass objects due to the ambiguity of whether they should be regarded as rogue planets or brown dwarfs. There are planetary-mass objects known to orbit brown dwarfs, such as 2M1207b,2MASS J044144b and Oph 98 B.
The 13-Jupiter-mass cutoff is a rule of thumb rather than a quantity with precise physical significance. Larger objects will burn most of their deuterium and smaller ones will burn only a little, and the 13Jupiter-mass value is somewhere in between. The amount of deuterium burnt also depends to some extent on the composition of the object, specifically on the amount of helium and deuterium present and on the fraction of heavier elements, which determines the atmospheric opacity and thus the radiative cooling rate.
As of 2011 the Extrasolar Planets Encyclopaedia included objects up to 25 Jupiter masses, saying, "The fact that there is no special feature around in the observed mass spectrum reinforces the choice to forget this mass limit". As of 2016, this limit was increased to 60 Jupiter masses, based on a study of mass–density relationships.
The Exoplanet Data Explorer includes objects up to 24 Jupiter masses with the advisory: "The 13 Jupiter-mass distinction by the IAU Working Group is physically unmotivated for planets with rocky cores, and observationally problematic due to the sin i ambiguity." The NASA Exoplanet Archive includes objects with a mass (or minimum mass) equal to or less than 30 Jupiter masses.
Sub-brown dwarf
Objects below , called sub-brown dwarfs or planetary-mass brown dwarfs, form in the same manner as stars and brown dwarfs (i.e. through the collapse of a gas cloud) but have a mass below the limiting mass for thermonuclear fusion of deuterium. | Brown dwarf | Wikipedia | 497 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
Some researchers call them free-floating planets, whereas others call them planetary-mass brown dwarfs.
Role of other physical properties in the mass estimate
While spectroscopic features can help to distinguish between low-mass stars and brown dwarfs, it is often necessary to estimate the mass to come to a conclusion. The theory behind the mass estimate is that brown dwarfs with a similar mass form in a similar way and are hot when they form. Some have spectral types that are similar to low-mass stars, such as 2M1101AB. As they cool down the brown dwarfs should retain a range of luminosities depending on the mass. Without the age and luminosity, a mass estimate is difficult; for example, an L-type brown dwarf could be an old brown dwarf with a high mass (possibly a low-mass star) or a young brown dwarf with a very low mass. For Y dwarfs this is less of a problem, as they remain low-mass objects near the sub-brown dwarf limit, even for relatively high age estimates. For L and T dwarfs it is still useful to have an accurate age estimate. The luminosity is here the less concerning property, as this can be estimated from the spectral energy distribution. The age estimate can be done in two ways. Either the brown dwarf is young and still has spectral features that are associated with youth, or the brown dwarf co-moves with a star or stellar group (star cluster or association), where age estimates are easier to obtain. A very young brown dwarf that was further studied with this method is 2M1207 and the companion 2M1207b. Based on the location, proper motion and spectral signature, this object was determined to belong to the ~8-million-year-old TW Hydrae association, and the mass of the secondary was determined to be 8 ± 2 , below the deuterium burning limit. An example of a very old age obtained by the co-movement method is the brown dwarf + white dwarf binary COCONUTS-1, with the white dwarf estimated to be billion years old. In this case the mass was not estimated with the derived age, but the co-movement provided an accurate distance estimate, using Gaia parallax. Using this measurement the authors estimated the radius, which was then used to estimate the mass for the brown dwarf as .
Observations
Classification of brown dwarfs
Spectral class M | Brown dwarf | Wikipedia | 488 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
These are brown dwarfs with a spectral class of M5.5 or later; they are also called late-M dwarfs. Some scientists regard them as red dwarfs. All brown dwarfs with spectral type M are young objects, such as Teide 1, which is the first M-type brown dwarf discovered, and LP 944-20, the closest M-type brown dwarf.
Spectral class L
The defining characteristic of spectral class M, the coolest type in the long-standing classical stellar sequence, is an optical spectrum dominated by absorption bands of titanium(II) oxide (TiO) and vanadium(II) oxide (VO) molecules. However, GD 165B, the cool companion to the white dwarf GD 165, had none of the hallmark TiO features of M dwarfs. The subsequent identification of many objects like GD 165B ultimately led to the definition of a new spectral class, the L dwarfs, defined in the red optical region of the spectrum not by metal-oxide absorption bands (TiO, VO), but by metal hydride emission bands (FeH, CrH, MgH, CaH) and prominent atomic lines of alkali metals (Na, K, Rb, Cs). , over 900 L dwarfs had been identified, most by wide-field surveys: the Two Micron All Sky Survey (2MASS), the Deep Near Infrared Survey of the Southern Sky (DENIS), and the Sloan Digital Sky Survey (SDSS). This spectral class also contains the coolest main-sequence stars (> 80 MJ), which have spectral classes L2 to L6.
Spectral class T | Brown dwarf | Wikipedia | 334 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
As GD 165B is the prototype of the L dwarfs, Gliese 229B is the prototype of a second new spectral class, the T dwarfs. T dwarfs are pinkish-magenta. Whereas near-infrared (NIR) spectra of L dwarfs show strong absorption bands of H2O and carbon monoxide (CO), the NIR spectrum of Gliese 229B is dominated by absorption bands from methane (CH4), a feature which in the Solar System is found only in the giant planets and Titan. CH4, H2O, and molecular hydrogen (H2) collision-induced absorption (CIA) give Gliese 229B blue near-infrared colors. Its steeply sloped red optical spectrum also lacks the FeH and CrH bands that characterize L dwarfs and instead is influenced by exceptionally broad absorption features from the alkali metals Na and K. These differences led J. Davy Kirkpatrick to propose the T spectral class for objects exhibiting H- and K-band CH4 absorption. , 355 T dwarfs were known. NIR classification schemes for T dwarfs have recently been developed by Adam Burgasser and Tom Geballe. Theory suggests that L dwarfs are a mixture of very-low-mass stars and sub-stellar objects (brown dwarfs), whereas the T dwarf class is composed entirely of brown dwarfs. Because of the absorption of sodium and potassium in the green part of the spectrum of T dwarfs, the actual appearance of T dwarfs to human visual perception is estimated to be not brown, but magenta. Early observations limited how distant T-dwarfs could be observed. T-class brown dwarfs, such as WISE 0316+4307, have been detected more than 100 light-years from the Sun. Observations with JWST have detected T-dwarfs such as UNCOVER-BD-1 up to 4500 parsec distant from the sun.
Spectral class Y | Brown dwarf | Wikipedia | 388 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
In 2009, the coolest-known brown dwarfs had estimated effective temperatures between , and have been assigned the spectral class T9. Three examples are the brown dwarfs CFBDS J005910.90–011401.3, ULAS J133553.45+113005.2 and ULAS J003402.77−005206.7. The spectra of these objects have absorption peaks around 1.55 micrometres. Delorme et al. have suggested that this feature is due to absorption from ammonia and that this should be taken as indicating the T–Y transition, making these objects of type Y0. However, the feature is difficult to distinguish from absorption by water and methane, and other authors have stated that the assignment of class Y0 is premature.
The first JWST spectral energy distribution of a Y-dwarf was able to observe several bands of molecules in the atmosphere of the Y0-dwarf WISE 0359−5401. The observations covered spectroscopy from 1 to 12 μm and photometry at 15, 18 and 21 μm. The molecules water (H2O), methane (CH4), carbon monoxide (CO), carbon dioxide (CO2) and ammonia (NH3) were detected in WISE 0359−5401. Many of these features have been observed before in this Y-dwarf and warmer T-dwarfs by other observatories, but JWST was able to observe them in a single spectrum. Methane is the main reservoir of carbon in the atmosphere of WISE 0359−5401, but there is still enough carbon left to form detectable carbon monoxide (at 4.5–5.0 μm) and carbon dioxide (at 4.2–4.35 μm) in the Y-dwarf. Ammonia was difficult to detect before JWST, as it blends in with the absorption feature of water in the near-infrared, as well at 5.5–7.1 μm. At longer wavelengths of 8.5–12 μm the spectrum of WISE 0359−5401 is dominated by the absorption of ammonia. At 3 μm there is an additional newly detected ammonia feature.
Role of vertical mixing | Brown dwarf | Wikipedia | 457 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
In the hydrogen-dominated atmosphere of brown dwarfs a chemical equilibrium between carbon monoxide and methane exists. Carbon monoxide reacts with hydrogen molecules and forms methane and hydroxyl in this reaction. The hydroxyl radical might later react with hydrogen and form water molecules. In the other direction of the reaction, methane reacts with hydroxyl and forms carbon monoxide and hydrogen. The chemical reaction is tilted towards carbon monoxide at higher temperatures (L-dwarfs) and lower pressure. At lower temperatures (T-dwarfs) and higher pressure the reaction is tilted towards methane, and methane predominates at the T/Y-boundary. However, vertical mixing of the atmosphere can cause methane to sink into lower layers of the atmosphere and carbon monoxide to rise from these lower and hotter layers. The carbon monoxide is slow to react back into methane because of an energy barrier that prevents the breakdown of the C-O bonds. This forces the observable atmosphere of a brown dwarf to be in a chemical disequilibrium. The L/T transition is mainly defined with the transition from a carbon-monoxide-dominated atmosphere in L-dwarfs to a methane-dominated atmosphere in T-dwarfs. The amount of vertical mixing can therefore push the L/T-transition to lower or higher temperatures. This becomes important for objects with modest surface gravity and extended atmospheres, such as giant exoplanets. This pushes the L/T transition to lower temperatures for giant exoplanets. For brown dwarfs this transition occurs at around 1200 K. The exoplanet HR 8799c, on the other hand, does not show any methane, while having a temperature of 1100K.
The transition between T- and Y-dwarfs is often defined as 500 K because of the lack of spectral observations of these cold and faint objects. Future observations with JWST and the ELTs might improve the sample of Y-dwarfs with observed spectra. Y-dwarfs are dominated by deep spectral features of methane, water vapor and possibly absorption features of ammonia and water ice. Vertical mixing, clouds, metallicity, photochemistry, lightning, impact shocks and metallic catalysts might influence the temperature at which the L/T and T/Y transition occurs.
Secondary features | Brown dwarf | Wikipedia | 456 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
Young brown dwarfs have low surface gravities because they have larger radii and lower masses than the field stars of similar spectral type. These sources are noted by a letter beta (β) for intermediate surface gravity or gamma (γ) for low surface gravity. Indicators of low surface gravity include weak CaH, K I and Na I lines, as well as a strong VO line. Alpha (α) denotes normal surface gravity and is usually dropped. Sometimes an extremely low surface gravity is denoted by a delta (δ). The suffix "pec" stands for "peculiar"; this suffix is still used for other features that are unusual, and summarizes different properties, indicating low surface gravity, subdwarfs and unresolved binaries. The prefix sd stands for subdwarf and only includes cool subdwarfs. This prefix indicates a low metallicity and kinematic properties that are more similar to halo stars than to disk stars. Subdwarfs appear bluer than disk objects. The red suffix describes objects with red color, but an older age. This is not interpreted as low surface gravity, but as a high dust content. The blue suffix describes objects with blue near-infrared colors that cannot be explained with low metallicity. Some are explained as L+T binaries, others are not binaries, such as 2MASS J11263991−5003550 and are explained with thin and/or large-grained clouds.
Spectral and atmospheric properties of brown dwarfs
The majority of flux emitted by L and T dwarfs is in the 1- to 2.5-micrometre near-infrared range. Low and decreasing temperatures through the late-M, -L, and -T dwarf sequence result in a rich near-infrared spectrum containing a wide variety of features, from relatively narrow lines of neutral atomic species to broad molecular bands, all of which have different dependencies on temperature, gravity, and metallicity. Furthermore, these low temperature conditions favor condensation out of the gas state and the formation of grains.
Typical atmospheres of known brown dwarfs range in temperature from 2200 down to . Compared to stars, which warm themselves with steady internal fusion, brown dwarfs cool quickly over time; more massive dwarfs cool more slowly than less massive ones. There is some evidence that the cooling of brown dwarfs slows down at the transition between spectral classes L and T (about 1000 K). | Brown dwarf | Wikipedia | 493 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
Observations of known brown dwarf candidates have revealed a pattern of brightening and dimming of infrared emissions that suggests relatively cool, opaque cloud patterns obscuring a hot interior that is stirred by extreme winds. The weather on such bodies is thought to be extremely strong, comparable to but far exceeding Jupiter's famous storms.
On January 8, 2013, astronomers using NASA's Hubble and Spitzer space telescopes probed the stormy atmosphere of a brown dwarf named 2MASS J22282889–4310262, creating the most detailed "weather map" of a brown dwarf thus far. It shows wind-driven, planet-sized clouds. The new research is a stepping stone toward a better understanding not only brown dwarfs, but also of the atmospheres of planets beyond the Solar System.
In April 2020 scientists reported measuring wind speeds of (up to 1,450 miles per hour) on the nearby brown dwarf 2MASS J10475385+2124234. To calculate the measurements, scientists compared the rotational movement of atmospheric features, as ascertained by brightness changes, against the electromagnetic rotation generated by the brown dwarf's interior. The results confirmed previous predictions that brown dwarfs would have high winds. Scientists are hopeful that this comparison method can be used to explore the atmospheric dynamics of other brown dwarfs and extrasolar planets.
Observational techniques
Coronagraphs have recently been used to detect faint objects orbiting bright visible stars, including Gliese 229B.
Sensitive telescopes equipped with charge-coupled devices (CCDs) have been used to search distant star clusters for faint objects, including Teide 1.
Wide-field searches have identified individual faint objects, such as Kelu-1 (30 light-years away).
Brown dwarfs are often discovered in surveys to discover exoplanets. Methods of detecting exoplanets work for brown dwarfs as well, although brown dwarfs are much easier to detect.
Brown dwarfs can be powerful emitters of radio emission due to their strong magnetic fields. Observing programs at the Arecibo Observatory and the Very Large Array have detected over a dozen such objects, which are also called ultracool dwarfs because they share common magnetic properties with other objects in this class. The detection of radio emission from brown dwarfs permits their magnetic field strengths to be measured directly. | Brown dwarf | Wikipedia | 462 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
Milestones
1995: First brown dwarf verified. Teide 1, an M8 object in the Pleiades cluster, is picked out with a CCD in the Spanish Observatory of Roque de los Muchachos of the Instituto de Astrofísica de Canarias.
First methane brown dwarf verified. Gliese 229B is discovered orbiting red dwarf Gliese 229A (20 ly away) using an adaptive optics coronagraph to sharpen images from the reflecting telescope at Palomar Observatory on Southern California's Mount Palomar; follow-up infrared spectroscopy made with their Hale Telescope shows an abundance of methane.
1998: First X-ray-emitting brown dwarf found. Cha Helpha 1, an M8 object in the Chamaeleon I dark cloud, is determined to be an X-ray source, similar to convective late-type stars.
15 December 1999: First X-ray flare detected from a brown dwarf. A team at the University of California monitoring LP 944-20 (, 16 ly away) via the Chandra X-ray Observatory, catches a 2-hour flare.
27 July 2000: First radio emission (in flare and quiescence) detected from a brown dwarf. A team of students at the Very Large Array detected emission from LP 944–20.
30 April 2004: First detection of a candidate exoplanet around a brown dwarf: 2M1207b discovered with the VLT and the first directly imaged exoplanet.
20 March 2013: Discovery of the closest brown dwarf system: Luhman 16.
25 April 2014: Coldest-known brown dwarf discovered. WISE 0855−0714 is 7.2 light-years away (seventh-closest system to the Sun) and has a temperature between −48 and −13 °C.
Brown dwarfs X-ray sources | Brown dwarf | Wikipedia | 376 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
X-ray flares detected from brown dwarfs since 1999 suggest changing magnetic fields within them, similar to those in very-low-mass stars. Although they do not fuse hydrogen into helium in their cores like stars, energy from the fusion of deuterium and gravitational contraction keep their interiors warm and generate strong magnetic fields. The interior of a brown dwarf is in a rapidly boiling, or convective state. When combined with the rapid rotation that most brown dwarfs exhibit, convection sets up conditions for the development of a strong, tangled magnetic field near the surface. The magnetic fields that generated the flare observed by Chandra from LP 944-20 has its origin in the turbulent magnetized plasma beneath the brown dwarf's "surface".
Using NASA's Chandra X-ray Observatory, scientists have detected X-rays from a low-mass brown dwarf in a multiple star system. This is the first time that a brown dwarf this close to its parent star(s) (Sun-like stars TWA 5A) has been resolved in X-rays. "Our Chandra data show that the X-rays originate from the brown dwarf's coronal plasma which is some 3 million degrees Celsius", said Yohko Tsuboi of Chuo University in Tokyo. "This brown dwarf is as bright as the Sun today in X-ray light, while it is fifty times less massive than the Sun", said Tsuboi. "This observation, thus, raises the possibility that even massive planets might emit X-rays by themselves during their youth!"
Brown dwarfs as radio sources | Brown dwarf | Wikipedia | 322 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
The first brown dwarf that was discovered to emit radio signals was LP 944-20, which was observed since it is also a source of X-ray emission, and both types of emission are signatures of coronae. Approximately 5–10% of brown dwarfs appear to have strong magnetic fields and emit radio waves, and there may be as many as 40 magnetic brown dwarfs within 25 pc of the Sun based on Monte Carlo modeling and their average spatial density. The power of the radio emissions of brown dwarfs is roughly constant despite variations in their temperatures. Brown dwarfs may maintain magnetic fields of up to 6 kG in strength. Astronomers have estimated brown dwarf magnetospheres to span an altitude of approximately 107 m given properties of their radio emissions. It is unknown whether the radio emissions from brown dwarfs more closely resemble those from planets or stars. Some brown dwarfs emit regular radio pulses, which are sometimes interpreted as radio emission beamed from the poles but may also be beamed from active regions. The regular, periodic reversal of radio wave orientation may indicate that brown dwarf magnetic fields periodically reverse polarity. These reversals may be the result of a brown dwarf magnetic activity cycle, similar to the solar cycle.
The first brown dwarf of spectral class M found to emit radio waves was LP 944-20, detected in 2001. The first brown dwarf of spectral class L found to emit radio waves was 2MASS J0036159+182110, detected in 2008. The first brown dwarf of spectral class T found to emit radio waves was 2MASS J10475385+2124234. This last discovery was significant since it revealed that brown dwarfs with temperatures similar to exoplanets could host strong >1.7 kG magnetic fields. Although a sensitive search for radio emission from Y dwarfs was conducted at the Arecibo Observatory in 2010, no emission was detected.
Recent developments
Estimates of brown dwarf populations in the solar neighbourhood suggest that there may be as many as six stars for every brown dwarf. A more recent estimate from 2017 using the young massive star cluster RCW 38 concluded that the Milky Way galaxy contains between 25 and 100 billion brown dwarfs. (Compare these numbers to the estimates of the number of stars in the Milky Way; 100 to 400 billion.) | Brown dwarf | Wikipedia | 457 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
In a study published in Aug 2017 NASA's Spitzer Space Telescope monitored infrared brightness variations in brown dwarfs caused by cloud cover of variable thickness. The observations revealed large-scale waves propagating in the atmospheres of brown dwarfs (similarly to the atmosphere of Neptune and other Solar System giant planets). These atmospheric waves modulate the thickness of the clouds and propagate with different velocities (probably due to differential rotation).
In August 2020, astronomers discovered 95 brown dwarfs near the Sun through the project Backyard Worlds: Planet 9.
In 2024 the James Webb Space Telescope provided the most detailed weather report yet on two brown dwarfs, revealing "stormy" conditions. These brown dwarfs, part of a binary star system named Luhman 16 discovered in 2013, are only 6.5 light-years away from Earth and are the closest brown dwarfs to our sun. Researchers discovered that they have turbulent clouds, likely made of silicate grains, with temperatures ranging from to . This indicates that hot sand is being blown by winds on the brown dwarfs. Additionally, absorption signatures of carbon monoxide, methane, and water vapor were detected.
Binary brown dwarfs
Brown dwarf–brown dwarf binaries
Brown dwarfs binaries of type M, L, and T are less common with a lower mass of the primary. L-dwarfs have a binary fraction of about % and the binary fraction for late T, early Y-dwarfs (T5-Y0) is about .
Brown dwarf binaries have a higher companion-to-host ratio for lower mass binaries. Binaries with a M-type star as a primary have for example a broad distribution of q with a preference of q ≥ 0.4. Brown dwarfs on the other hand show a strong preference for q ≥ 0.7. The separation is decreasing with mass: M-type stars have a separation peaking at 3–30 astronomical units (au), M-L-type brown dwarfs have a projected separation peaking at 5–8 au and T5–Y0 objects have a projected separation that follows a lognormal distribution with a peak separation of about 2.9 au.
An example is the closest brown dwarf binary Luhman 16 AB with a primary L7.5 dwarf and a separation of 3.5 au and q = 0.85. The separation is on the lower end of the expected separation for M-L-type brown dwarfs, but the mass ratio is typical. | Brown dwarf | Wikipedia | 492 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
It is not known if the same trend continues with Y-dwarfs, because their sample size is so small. The Y+Y dwarf binaries should have a high mass ratio q and a low separation, reaching scales of less than one au. In 2023, the Y+Y dwarf WISE J0336-0143 was confirmed as a binary with JWST, with a mass ratio of q=0.62±0.05 and a separation of 0.97 astronomical units. The researchers point out that the sample size of low-mass binary brown dwarfs is too small to determine if WISE J0336-0143 is a typical representative of low-mass binaries or a peculiar system.
Observations of the orbit of binary systems containing brown dwarfs can be used to measure the mass of the brown dwarf. In the case of 2MASSW J0746425+2000321, the secondary weighs 6% of the solar mass. This measurement is called a dynamical mass. The brown dwarf system closest to the Solar System is the binary Luhman 16. It was attempted to search for planets around this system with a similar method, but none were found.
Unusual brown dwarf binaries
The wide binary system 2M1101AB was the first binary with a separation greater than . The discovery of the system gave definitive insights to the formation of brown dwarfs. It was previously thought that wide binary brown dwarfs are not formed or at least are disrupted at ages of 1–10 Myr. The existence of this system is also inconsistent with the ejection hypothesis. The ejection hypothesis was a proposed hypothesis in which brown dwarfs form in a multiple system, but are ejected before they gain enough mass to burn hydrogen.
More recently the wide binary W2150AB was discovered. It has a similar mass ratio and binding energy as 2M1101AB, but a greater age and is located in a different region of the galaxy. While 2M1101AB is in a closely crowded region, the binary W2150AB is in a sparsely-separated field. It must have survived any dynamical interactions in its natal star cluster. The binary belongs also to a few L+T binaries that can be easily resolved by ground-based observatories. The other two are SDSS J1416+13AB and Luhman 16. | Brown dwarf | Wikipedia | 477 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
There are other interesting binary systems such as the eclipsing binary brown dwarf system 2MASS J05352184–0546085. Photometric studies of this system have revealed that the less massive brown dwarf in the system is hotter than its higher-mass companion.
Brown dwarfs around stars
Brown dwarfs and massive planets in a close orbit (less than 5 au) around stars are rare and this is sometimes described as the brown dwarf desert. Less than 1% of stars with the mass of the sun have a brown dwarf within 3–5 au.
An example for a star–brown dwarf binary is the first discovered T-dwarf Gliese 229 B, which orbits around the main-sequence star Gliese 229 A, a red dwarf. Brown dwarfs orbiting subgiants are also known, such as TOI-1994b which orbits its star every 4.03 days.
There is also disagreement if some low-mass brown dwarfs should be considered planets. The NASA Exoplanet archive includes brown dwarfs with a minimum mass less or equal to 30 Jupiter masses as planets as long as there are other criteria fulfilled (e.g. orbiting a star). The Working Group on Extrasolar Planets (WGESP) of the IAU on the other hand only considers planets with a mass below 13 Jupiter masses.
White dwarf–brown dwarf binaries
Brown dwarfs around white dwarfs are quite rare. GD 165 B, the prototype of the L dwarfs, is one such system. Such systems can be useful in determining the age of the system and the mass of the brown dwarf. Other white dwarf-brown dwarf binaries are COCONUTS-1 AB (7 billion years old), and LSPM J0055+5948 AB (10 billion years old), SDSS J22255+0016 AB (2 billion years old) WD 0806−661 AB (1.5–2.7 billion years old). | Brown dwarf | Wikipedia | 398 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
Systems with close, tidally locked brown dwarfs orbiting around white dwarfs belong to the post common envelope binaries or PCEBs. Only eight confirmed PCEBs containing a white dwarf with a brown dwarf companion are known, including WD 0137-349 AB. In the past history of these close white dwarf–brown dwarf binaries, the brown dwarf is engulfed by the star in the red giant phase. Brown dwarfs with a mass lower than 20 Jupiter masses would evaporate during the engulfment. The dearth of brown dwarfs orbiting close to white dwarfs can be compared with similar observations of brown dwarfs around main-sequence stars, described as the brown-dwarf desert. The PCEB might evolve into a cataclysmic variable star (CV*) with the brown dwarf as the donor. Simulations have shown that highly evolved CV* are mostly associated with substellar donors (up to 80%). A type of CV*, called WZ Sge-type dwarf nova often show donors with a mass near the borderline of low-mass stars and brown dwarfs. The binary BW Sculptoris is such a dwarf nova with a brown dwarf donor. This brown dwarf likely formed when a donor star lost enough mass to become a brown dwarf. The mass loss comes with a loss of the orbital period until it reaches a minimum of 70–80 minutes at which the period increases again. This gives this evolutionary stage the name period bouncer. There could also exist brown dwarfs that merged with white dwarfs. The nova CK Vulpeculae might be a result of such a white dwarf–brown dwarf merger.
Formation and evolution
The earliest stage of brown dwarf formation is called proto- or pre-brown dwarf. Proto-brown dwarfs are low-mass equivalents of protostars (class 0/I objects). Additionally Very Low Luminosity Objects (VeLLOs) that have Lint ≤0.1-0.2 are often proto-brown dwarfs. They are found in nearby star-forming clouds. Around 67 promising proto-brown dwarfs and 26 pre-brown dwarfs are known as of 2024. As of 2017 there is only one known proto-brown dwarf that is connected with a large Herbig–Haro object. This is the brown dwarf Mayrit 1701117, which is surrounded by a pseudo-disk and a Keplerian disk. Mayrit 1701117 launches the 0.7-light-year-long jet HH 1165, mostly seen in ionized sulfur. | Brown dwarf | Wikipedia | 509 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
Brown dwarfs form similarly to stars and are surrounded by protoplanetary disks, such as Cha 110913−773444. Disks around brown dwarfs have been found to have many of the same features as disks around stars; therefore, it is expected that there will be accretion-formed planets around brown dwarfs. Given the small mass of brown dwarf disks, most planets will be terrestrial planets rather than gas giants. If a giant planet orbits a brown dwarf across our line of sight, then, because they have approximately the same diameter, this would give a large signal for detection by transit. The accretion zone for planets around a brown dwarf is very close to the brown dwarf itself, so tidal forces would have a strong effect.
In 2020, the closest brown dwarf with an associated primordial disk (class II disk)—WISEA J120037.79-784508.3 (W1200-7845)—was discovered by the Disk Detective project when classification volunteers noted its infrared excess. It was vetted and analyzed by the science team who found that W1200-7845 had a 99.8% probability of being a member of the ε Chamaeleontis (ε Cha) young moving group association. Its parallax (using Gaia DR2 data) puts it at a distance of 102 parsecs (or 333 lightyears) from Earth—which is within the local Solar neighborhood. | Brown dwarf | Wikipedia | 295 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
A paper from 2021 studied circumstellar discs around brown dwarfs in stellar associations that are a few million years old and 140 to 200 parsecs away. The researchers found that these disks are not massive enough to form planets in the future. There is evidence in these disks that might indicate that planet formation begins at earlier stages and that planets are already present in these disks. The evidence for disk evolution includes a decreasing disk mass over time, dust grain growth and dust settling. Two brown dwarf disks were also found in absorption and at least 4 disks are photoevaporating from external UV-ratiation in the Orion Nebula. Such objects are also called proplyds. Proplyd 181−247, which is a brown dwarf or low-mass star, is surrounded by a disk with a radius of 30 astronomical units and the disk has a mass of 6.2±1.0 . Disks around brown dwarfs usually have a radius smaller than 40 astronomical units, but three disks in the more distant Taurus molecular cloud have a radius larger than 70 au and were resolved with ALMA. These larger disks are able to form rocky planets with a mass >1 . There are also brown dwarfs with disks in associations older than a few million years, which might be evidence that disks around brown dwarfs need more time to dissipate. Especially old disks (>20 Myrs) are sometimes called Peter Pan disks. Currently 2MASS J02265658-5327032 is the only known brown dwarf that has a Peter Pan disk.
The brown dwarf Cha 110913−773444, located 500 light-years away in the constellation Chamaeleon, may be in the process of forming a miniature planetary system. Astronomers from Pennsylvania State University have detected what they believe to be a disk of gas and dust similar to the one hypothesized to have formed the Solar System. Cha 110913−773444 is the smallest brown dwarf found to date (), and if it formed a planetary system, it would be the smallest-known object to have one.
Planets around brown dwarfs | Brown dwarf | Wikipedia | 428 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
According to the IAU working definition (from August 2018) an exoplanet can orbit a brown dwarf. It requires a mass below 13 and a mass ratio of M/Mcentral<2/(25+√621). This means that an object with a mass up to 3.2 around a brown dwarf with a mass of 80 is considered a planet. It also means that an object with a mass up to 0.52 around a brown dwarf with a mass of 13 is considered a planet.
The super-Jupiter planetary-mass objects 2M1207b, 2MASS J044144 and Oph 98 B that are orbiting brown dwarfs at large orbital distances may have formed by cloud collapse rather than accretion and so may be sub-brown dwarfs rather than planets, which is inferred from relatively large masses and large orbits. The first discovery of a low-mass companion orbiting a brown dwarf (ChaHα8) at a small orbital distance using the radial velocity technique paved the way for the detection of planets around brown dwarfs on orbits of a few AU or smaller. However, with a mass ratio between the companion and primary in ChaHα8 of about 0.3, this system rather resembles a binary star. Then, in 2008, the first planetary-mass companion in a relatively small orbit (MOA-2007-BLG-192Lb) was discovered orbiting a brown dwarf.
Planets around brown dwarfs are likely to be carbon planets depleted of water. | Brown dwarf | Wikipedia | 307 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
A 2017 study, based upon observations with Spitzer estimates that 175 brown dwarfs need to be monitored in order to guarantee (95%) at least one detection of a below earth-sized planet via the transiting method. JWST could potentially detect smaller planets. The orbits of planets and moons in the solar system often align with the orientation of the host star/planet they orbit. Assuming the orbit of a planet is aligned with the rotational axis of a brown dwarf or planetary-mass object, the geometric transit probability of an object similar to Io can be calculated with the formula cos(79.5°)/cos(inclination). The inclination was estimated for several brown dwarfs and planetary-mass objects. SIMP 0136 for example has an estimated inclination of 80°±12. Assuming the lower bound of i≥68° for SIMP 0136, this results in a transit probability of ≥48.6% for close-in planets. It is however not known how common close-in planets are around brown dwarfs and they might be more common for lower-mass objects, as disk sizes seem to decrease with mass.
Habitability
Habitability for hypothetical planets orbiting brown dwarfs has been studied. Computer models suggesting conditions for these bodies to have habitable planets are very stringent, the habitable zone being narrow, close (T dwarf 0.005 au) and decreasing with time, due to the cooling of the brown dwarf (they fuse for at most 10 million years). The orbits there would have to be of extremely low eccentricity (on the order of 10 to the minus 6) to avoid strong tidal forces that would trigger a runaway greenhouse effect on the planets, rendering them uninhabitable. There would also be no moons.
Superlative brown dwarfs
In 1984, it was postulated by some astronomers that the Sun may be orbited by an undetected brown dwarf (sometimes referred to as Nemesis) that could interact with the Oort cloud just as passing stars can. However, this hypothesis has fallen out of favor.
Table of firsts
Table of extremes | Brown dwarf | Wikipedia | 422 | 44401 | https://en.wikipedia.org/wiki/Brown%20dwarf | Physical sciences | Stellar astronomy | null |
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