text stringlengths 8 3.87k |
|---|
58.6644287109375 57 WikiText2 |
23400 = = = = Binary stars = = = = |
114.2520751953125 10 WikiText2 |
23401 The post – main @-@ sequence evolution of binary stars may be significantly different from the evolution of single stars of the same mass . If stars in a binary system are sufficiently close , when one of the stars expands to become a red giant it may overflow its Roche lobe , the region around a star where mate... |
57.71751022338867 111 WikiText2 |
23402 = = Distribution = = |
914.49609375 5 WikiText2 |
23403 In addition to isolated stars , a multi @-@ star system can consist of two or more gravitationally bound stars that orbit each other . The simplest and most common multi @-@ star system is a binary star , but systems of three or more stars are also found . For reasons of orbital stability , such multi @-@ star s... |
26.475217819213867 117 WikiText2 |
23404 It has been a long @-@ held assumption that the majority of stars occur in gravitationally bound , multiple @-@ star systems . This is particularly true for very massive O and B class stars , where 80 % of the stars are believed to be part of multiple @-@ star systems . The proportion of single star systems incr... |
34.07301330566406 108 WikiText2 |
23405 Stars are not spread uniformly across the universe , but are normally grouped into galaxies along with interstellar gas and dust . A typical galaxy contains hundreds of billions of stars , and there are more than 100 billion ( 1011 ) galaxies in the observable universe . In 2010 , one estimate of the number of s... |
18.94883918762207 89 WikiText2 |
23406 The nearest star to the Earth , apart from the Sun , is Proxima Centauri , which is 39 @.@ 9 trillion kilometres , or 4 @.@ 2 light @-@ years . Travelling at the orbital speed of the Space Shuttle ( 8 kilometres per second — almost 30 @,@ 000 kilometres per hour ) , it would take about 150 @,@ 000 years to arriv... |
52.96474075317383 113 WikiText2 |
23407 Due to the relatively vast distances between stars outside the galactic nucleus , collisions between stars are thought to be rare . In denser regions such as the core of globular clusters or the galactic center , collisions can be more common . Such collisions can produce what are known as blue stragglers . Thes... |
30.320621490478516 80 WikiText2 |
23408 = = Characteristics = = |
503.3805236816406 5 WikiText2 |
23409 Almost everything about a star is determined by its initial mass , including such characteristics as luminosity , size , evolution , lifespan , and its eventual fate . |
63.85992431640625 29 WikiText2 |
23410 = = = Age = = = |
122.2681655883789 7 WikiText2 |
23411 Most stars are between 1 billion and 10 billion years old . Some stars may even be close to 13 @.@ 8 billion years old — the observed age of the universe . The oldest star yet discovered , HD 140283 , nicknamed Methuselah star , is an estimated 14 @.@ 46 ± 0 @.@ 8 billion years old . ( Due to the uncertainty in ... |
37.74088668823242 109 WikiText2 |
23412 The more massive the star , the shorter its lifespan , primarily because massive stars have greater pressure on their cores , causing them to burn hydrogen more rapidly . The most massive stars last an average of a few million years , while stars of minimum mass ( red dwarfs ) burn their fuel very slowly and can... |
23.897554397583008 68 WikiText2 |
23413 = = = Chemical composition = = = |
174.91847229003906 8 WikiText2 |
23414 When stars form in the present Milky Way galaxy they are composed of about 71 % hydrogen and 27 % helium , as measured by mass , with a small fraction of heavier elements . Typically the portion of heavy elements is measured in terms of the iron content of the stellar atmosphere , as iron is a common element and... |
30.31134033203125 90 WikiText2 |
23415 The star with the lowest iron content ever measured is the dwarf HE1327 @-@ 2326 , with only 1 / 200,000th the iron content of the Sun . By contrast , the super @-@ metal @-@ rich star μ Leonis has nearly double the abundance of iron as the Sun , while the planet @-@ bearing star 14 Herculis has nearly triple th... |
66.68559265136719 115 WikiText2 |
23416 = = = Diameter = = = |
98.83454895019531 7 WikiText2 |
23417 Due to their great distance from the Earth , all stars except the Sun appear to the unaided eye as shining points in the night sky that twinkle because of the effect of the Earth 's atmosphere . The Sun is also a star , but it is close enough to the Earth to appear as a disk instead , and to provide daylight . O... |
35.09823989868164 94 WikiText2 |
23418 The disks of most stars are much too small in angular size to be observed with current ground @-@ based optical telescopes , and so interferometer telescopes are required to produce images of these objects . Another technique for measuring the angular size of stars is through occultation . By precisely measuring... |
41.030235290527344 88 WikiText2 |
23419 Stars range in size from neutron stars , which vary anywhere from 20 to 40 km ( 25 mi ) in diameter , to supergiants like Betelgeuse in the Orion constellation , which has a diameter approximately 1 @,@ 070 times that of the Sun — about 1 @,@ 490 @,@ 171 @,@ 880 km ( 925 @,@ 949 @,@ 878 mi ) . Betelgeuse , howev... |
30.732351303100586 89 WikiText2 |
23420 = = = Kinematics = = = |
74.85884094238281 7 WikiText2 |
23421 The motion of a star relative to the Sun can provide useful information about the origin and age of a star , as well as the structure and evolution of the surrounding galaxy . The components of motion of a star consist of the radial velocity toward or away from the Sun , and the traverse angular movement , which... |
25.424541473388672 66 WikiText2 |
23422 Radial velocity is measured by the doppler shift of the star 's spectral lines , and is given in units of km / s . The proper motion of a star , its parallax , is determined by precise astrometric measurements in units of milli @-@ arc seconds ( mas ) per year . With knowledge of the star 's parallax and its dis... |
30.62247085571289 113 WikiText2 |
23423 When both rates of movement are known , the space velocity of the star relative to the Sun or the galaxy can be computed . Among nearby stars , it has been found that younger population I stars have generally lower velocities than older , population II stars . The latter have elliptical orbits that are inclined ... |
43.98981475830078 95 WikiText2 |
23424 = = = Magnetic field = = = |
109.7584228515625 8 WikiText2 |
23425 The magnetic field of a star is generated within regions of the interior where convective circulation occurs . This movement of conductive plasma functions like a dynamo , wherein the movement of elecrical charges induce magnetic fields , as does a mechanical dynamo . Those magnetic fields have a great range tha... |
40.741512298583984 173 WikiText2 |
23426 Young , rapidly rotating stars tend to have high levels of surface activity because of their magnetic field . The magnetic field can act upon a star 's stellar wind , functioning as a brake to gradually slow the rate of rotation with time . Thus , older stars such as the Sun have a much slower rate of rotation a... |
35.745845794677734 116 WikiText2 |
23427 = = = Mass = = = |
193.53993225097656 7 WikiText2 |
23428 One of the most massive stars known is Eta Carinae , which , with 100 – 150 times as much mass as the Sun , will have a lifespan of only several million years . Studies of the most massive open clusters suggests 150 M ☉ as an upper limit for stars in the current era of the universe . This represents an empirical... |
31.72781753540039 139 WikiText2 |
23429 The first stars to form after the Big Bang may have been larger , up to 300 M ☉ , due to the complete absence of elements heavier than lithium in their composition . This generation of supermassive population III stars is likely to have existed in the very early universe ( i.e. , they are observed to have a high... |
51.961753845214844 115 WikiText2 |
23430 With a mass only 80 times that of Jupiter ( MJ ) , 2MASS J0523 @-@ 1403 is the smallest known star undergoing nuclear fusion in its core . For stars with metallicity similar to the Sun , the theoretical minimum mass the star can have and still undergo fusion at the core , is estimated to be about 75 MJ . When th... |
61.475372314453125 115 WikiText2 |
23431 The combination of the radius and the mass of a star determines its surface gravity . Giant stars have a much lower surface gravity than do main sequence stars , while the opposite is the case for degenerate , compact stars such as white dwarfs . The surface gravity can influence the appearance of a star 's spec... |
38.2646484375 70 WikiText2 |
23432 = = = Rotation = = = |
150.1808624267578 7 WikiText2 |
23433 The rotation rate of stars can be determined through spectroscopic measurement , or more exactly determined by tracking their starspots . Young stars can have a rotation greater than 100 km / s at the equator . The B @-@ class star Achernar , for example , has an equatorial velocity of about 225 km / s or greate... |
44.6383056640625 166 WikiText2 |
23434 Degenerate stars have contracted into a compact mass , resulting in a rapid rate of rotation . However they have relatively low rates of rotation compared to what would be expected by conservation of angular momentum — the tendency of a rotating body to compensate for a contraction in size by increasing its rate... |
22.52556610107422 131 WikiText2 |
23435 = = = Temperature = = = |
136.86146545410156 7 WikiText2 |
23436 The surface temperature of a main sequence star is determined by the rate of energy production of its core and by its radius , and is often estimated from the star 's color index . The temperature is normally given in terms of an effective temperature , which is the temperature of an idealized black body that ra... |
28.844633102416992 106 WikiText2 |
23437 The stellar temperature will determine the rate of ionization of various elements , resulting in characteristic absorption lines in the spectrum . The surface temperature of a star , along with its visual absolute magnitude and absorption features , is used to classify a star ( see classification below ) . |
64.54361724853516 51 WikiText2 |
23438 Massive main sequence stars can have surface temperatures of 50 @,@ 000 K. Smaller stars such as the Sun have surface temperatures of a few thousand K. Red giants have relatively low surface temperatures of about 3 @,@ 600 K ; but they also have a high luminosity due to their large exterior surface area . |
39.58834457397461 60 WikiText2 |
23439 = = Radiation = = |
840.34765625 5 WikiText2 |
23440 The energy produced by stars , a product of nuclear fusion , radiates to space as both electromagnetic radiation and particle radiation . The particle radiation emitted by a star is manifested as the stellar wind , which streams from the outer layers as electrically charged protons and alpha and beta particles .... |
39.44099807739258 72 WikiText2 |
23441 The production of energy at the core is the reason stars shine so brightly : every time two or more atomic nuclei fuse together to form a single atomic nucleus of a new heavier element , gamma ray photons are released from the nuclear fusion product . This energy is converted to other forms of electromagnetic en... |
36.3424186706543 77 WikiText2 |
23442 The color of a star , as determined by the most intense frequency of the visible light , depends on the temperature of the star 's outer layers , including its photosphere . Besides visible light , stars also emit forms of electromagnetic radiation that are invisible to the human eye . In fact , stellar electrom... |
25.851457595825195 125 WikiText2 |
23443 Using the stellar spectrum , astronomers can also determine the surface temperature , surface gravity , metallicity and rotational velocity of a star . If the distance of the star is found , such as by measuring the parallax , then the luminosity of the star can be derived . The mass , radius , surface gravity ,... |
18.088645935058594 117 WikiText2 |
23444 = = = Luminosity = = = |
410.00665283203125 7 WikiText2 |
23445 The luminosity of a star is the amount of light and other forms of radiant energy it radiates per unit of time . It has units of power . The luminosity of a star is determined by its radius and surface temperature . Many stars do not radiate uniformly across their entire surface . The rapidly rotating star Vega ... |
24.440185546875 82 WikiText2 |
23446 Patches of the star 's surface with a lower temperature and luminosity than average are known as starspots . Small , dwarf stars such as our Sun generally have essentially featureless disks with only small starspots . Giant stars have much larger , more obvious starspots , and they also exhibit strong stellar li... |
70.00212860107422 85 WikiText2 |
23447 = = = Magnitude = = = |
609.4649658203125 7 WikiText2 |
23448 The apparent brightness of a star is expressed in terms of its apparent magnitude . It is a function of the star 's luminosity , its distance from Earth , and the altering of the star 's light as it passes through Earth 's atmosphere . Intrinsic or absolute magnitude is directly related to a star 's luminosity ,... |
27.871498107910156 94 WikiText2 |
23449 Both the apparent and absolute magnitude scales are logarithmic units : one whole number difference in magnitude is equal to a brightness variation of about 2 @.@ 5 times ( the 5th root of 100 or approximately 2 @.@ 512 ) . This means that a first magnitude star ( + 1 @.@ 00 ) is about 2 @.@ 5 times brighter tha... |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.