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Line 33: | header11 = Orbital characteristics | label12 = {{longitem|Mean distance from [[Milky Way]] core}} | data12 = 24,000 to 28,000 [[light-year]]s<ref name="francis14">{{cite journal |last1=Francis |first1=Charles |last2=Anderson |first2=Erik |date=June 2014 |title=Two estimates of the distance to the Galactic Centre |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=441 |issue=2 |pages=1105–1114 |arxiv=1309.2629 |bibcode=2014MNRAS.441.1105F |doi=10.1093/mnras/stu631 |s2cid=119235554}}</ref>
| label13 = [[Galactic year|Galactic period]] | data13 = 225–250 million [[julian year (astronomy)|years]] Line 117: }} The '''Sun''' is the [[star]] at the center of the [[Solar System]]. It is a massive, nearly perfect [[sphere]] of hot [[Plasma (physics)|plasma]], The Sun orbits the [[Galactic Center]] at a distance of 24,000 to 28,000 [[light-year]]s. The Sun is a [[G-type main-sequence star]] (G2V), informally called a [[G-type main-sequence star|yellow dwarf]], though its light is actually white. It formed approximately 4.6 billion<ref group=lower-alpha name=short>All numbers in this article are [[short scale]]. One billion is 10<sup>9</sup>, or 1,000,000,000. Every second, the Sun's core fuses about 600 billion [[kilograms]] (kg) of hydrogen into helium and converts 4 billion kg of [[mass–energy equivalence|matter into energy]]. Far in the future, when [[hydrogen fusion]] in the Sun's core diminishes to the point where the Sun is no longer in [[hydrostatic equilibrium]], its core will undergo a marked increase in density and temperature which will cause its outer layers to expand, eventually transforming the Sun into a [[red giant]]. This process will make the Sun large enough to render Earth uninhabitable approximately five billion years from the present. Subsequently, the Sun will shed its outer layers and become a dense type of cooling star (a [[white dwarf]]), and no longer produce energy by fusion, but it will still glow and give off heat from its previous fusion for trillions of years. After that, it is theorized to become a super dense [[black dwarf]], giving off no more energy. Line 133: == General characteristics == The Sun is a [[G-type main-sequence star]] that makes up about 99.86% of the mass of the Solar System.<ref name="Woolfson00">{{Cite journal |last=Woolfson |first=M. |date=2000 |title=The origin and evolution of the solar system |url=http://inis.jinr.ru/sl/vol1/_djvu/P_Physics/Woolfson%20M.M.%20Origin%20and%20evolution%20of%20the%20solar%20system%20(IOP)(425s).pdf |url-status=live |journal=[[Astronomy & Geophysics]] |volume=41 |issue=1 |page=12 |bibcode=2000A&G....41a..12W |doi=10.1046/j.1468-4004.2000.00012.x |archive-url=https://web.archive.org/web/20200711133403/http://inis.jinr.ru/sl/vol1/_djvu/P_Physics/Woolfson%20M.M.%20Origin%20and%20evolution%20of%20the%20solar%20system%20(IOP)(425s).pdf |archive-date=11 July 2020 |access-date=12 April 2020 |doi-access=free}}</ref><!-- There are several estimations on the mass of the Solar System; for further information please have a look at the talk page. --> It has an [[absolute magnitude]] of +4.83, estimated to be brighter than about 85% of the stars in the [[Milky Way]], most of which are [[red dwarf]]s.<ref>{{Cite news |last=Than |first=K. |date=2006 |title=Astronomers Had it Wrong: Most Stars are Single |publisher=Space.com |url=http://www.space.com/scienceastronomy/060130_mm_single_stars.html |url-status=live |access-date=1 August 2007 |archive-url=https://web.archive.org/web/20101221093125/http://www.space.com/scienceastronomy/060130_mm_single_stars.html |archive-date=21 December 2010}}</ref><ref>{{Cite journal |last=Lada |first=C. J. |year=2006 |title=Stellar multiplicity and the initial mass function: Most stars are single |journal=[[Astrophysical Journal Letters]] |volume=640 |issue=1 |pages=L63–L66 |arxiv=astro-ph/0601375 |bibcode=2006ApJ...640L..63L |doi=10.1086/503158 |s2cid=8400400}}</ref> The Sun is a [[Population I stars|Population I]], or heavy-element-rich,{{efn|name=heavy elements}} star.<ref name="zeilik">{{Cite book |last1=Zeilik |first1=M. A. |title=Introductory Astronomy & Astrophysics |last2=Gregory |first2=S. A. |year=1998 |publisher=Saunders College Publishing |isbn=978-0-03-006228-5 |edition=4th |page=322}}</ref> Its formation approximately 4.6 billion years ago may have been triggered by shockwaves from one or more nearby [[supernova]]e.<ref name="Connelly2012">{{Cite journal |last1=Connelly |first1=James N. |last2=Bizzarro |first2=Martin |last3=Krot |first3=Alexander N. |last4=Nordlund |first4=Åke |last5=Wielandt |first5=Daniel |last6=Ivanova |first6=Marina A. |date=2 November 2012 |title=The Absolute Chronology and Thermal Processing of Solids in the Solar Protoplanetary Disk |journal=[[Science (journal)|Science]] |volume=338 |issue=6107 |pages=651–655 |bibcode=2012Sci...338..651C |doi=10.1126/science.1226919 |pmid=23118187 |s2cid=21965292}}</ref><ref name="Falk">{{Cite journal |last1=Falk |first1=S. W. |last2=Lattmer |first2=J. M. |last3=Margolis |first3=S. H. |year=1977 |title=Are supernovae sources of presolar grains? |journal=[[Nature (journal)|Nature]] |volume=270 |issue=5639 |pages=700–701 |bibcode=1977Natur.270..700F |doi=10.1038/270700a0 |s2cid=4240932}}</ref> This is suggested by a high [[Abundance of the chemical elements|abundance]] of heavy elements in the Solar System, such as [[gold]] and [[uranium]], relative to the abundances of these elements in so-called [[Population II]], heavy-element-poor, stars. The heavy elements could most plausibly have been produced by [[endothermic]] nuclear reactions during a supernova, or by [[Nuclear transmutation|transmutation]] through [[neutron absorption]] within a massive second-generation star.<ref name="zeilik" /> The Sun is by far the [[List of brightest natural objects in the sky|brightest object in the Earth's sky]], with an [[apparent magnitude]] of −26.74.<ref>{{Cite journal |last=Burton |first=W. B. |date=1986 |title=Stellar parameters |journal=[[Space Science Reviews]] |volume=43 |issue=3–4 |pages=244–250 |doi=10.1007/BF00190626 |s2cid=189796439}}</ref><ref>{{Cite journal |last1=Bessell |first1=M. S. |last2=Castelli |first2=F. |last3=Plez |first3=B. |date=1998 |title=Model atmospheres broad-band colors, bolometric corrections and temperature calibrations for O–M stars |journal=[[Astronomy and Astrophysics]] |volume=333 |pages=231–250 |bibcode=1998A&A...333..231B}}</ref> This is about 13 billion times brighter than the next brightest star, [[Sirius]], which has an apparent magnitude of −1.46.<ref name="Hoffleit1991">{{cite book | chapter=HR 2491 | title=Bright Star Catalogue |edition= 5th Revised |last1=Hoffleit | first1=D. |author-link1=Dorrit Hoffleit |display-authors=etal | date=1991 | publisher=[[Centre de Données astronomiques de Strasbourg|CDS]] | url=http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HR%202491 |bibcode= 1991bsc..book.....H}}</ref> Line 155: Since the Sun formed, the main fusion process has involved fusing hydrogen into helium. Over the past 4.6 billion years, the amount of helium and its location within the Sun has gradually changed. The proportion of helium within the core has increased from about 24% to about 60% due to fusion, and some of the helium and heavy elements have settled from the photosphere toward the center of the Sun because of [[gravity]]. The proportions of heavier elements are unchanged. [[Heat transfer|Heat is transferred]] outward from the Sun's core by radiation rather than by convection (see [[#Radiative zone|Radiative zone]] below), so the fusion products are not lifted outward by heat; they remain in the core,<ref name=hkt2004_9.2.3>{{Cite book |last1=Hansen |first1=C. J. |last2=Kawaler |first2=S. A. |last3=Trimble |first3=V. |title=Stellar Interiors: Physical Principles, Structure, and Evolution |pages=§ 9.2.3 |no-pp=yes |edition=2nd |publisher=[[Springer Science+Business Media|Springer]] |year=2004 |isbn=978-0-387-20089-7}}</ref> and gradually an inner core of helium has begun to form that cannot be fused because presently the Sun's core is not hot or dense enough to fuse helium. In the current photosphere, the helium fraction is reduced, and the [[metallicity]] is only 84% of what it was in the [[Protostar|protostellar]] phase (before nuclear fusion in the core started). In the future, helium will continue to accumulate in the core, and in about 5 billion years this gradual build-up will eventually cause the Sun to exit the [[main sequence]] and become a [[red giant]].<ref>{{cite journal | last=Iben | first=Icko Jnr. | title=Stellar Evolution. II. The Evolution of a 3 M<sub>☉</sub> Star from the Main Sequence Through Core Helium Burning | journal=Astrophysical Journal | volume=142 | page=1447 | date=November 1965 | doi=10.1086/148429 | bibcode=1965ApJ...142.1447I }}</ref> The chemical composition of the photosphere is normally considered representative of the composition of the primordial Solar System.<ref name="aller1968">{{Cite journal |last=Aller |first=L. H. |title=The chemical composition of the Sun and the solar system |journal=Proceedings of the Astronomical Society of Australia |volume=1 |issue=4 |page=133 |date=1968 |bibcode=1968PASA....1..133A|doi=10.1017/S1323358000011048|s2cid=119759834 |doi-access=free }}</ref> Typically, the solar heavy-element abundances described above are measured both by using [[astronomical spectroscopy|spectroscopy]] of the Sun's photosphere and by measuring abundances in [[meteorites]] that have never been heated to melting temperatures. These meteorites are thought to retain the composition of the protostellar Sun and are thus not affected by the settling of heavy elements. The two methods generally agree well.<ref name="basu2008">{{Cite journal |last1=Basu |first1=S. |last2=Antia |first2=H. M. |year=2008 |title=Helioseismology and Solar Abundances |journal=[[Physics Reports]] |volume=457 |issue=5–6 |pages=217–283 |arxiv=0711.4590 |bibcode=2008PhR...457..217B |doi=10.1016/j.physrep.2007.12.002 |s2cid=119302796}}</ref> == Structure and fusion == | |||