Editing Solar luminosity (section)

{{Short description|Unit of light in stars and galaxies}}
[[File:Solar evolution (English).svg|right|thumb|upright=1.5|Evolution of the solar luminosity, [[Solar radius|radius]] and [[effective temperature]] compared to the present-day Sun. After Ribas (2010)<ref name=ribas2010>{{citation | last=Ribas | first=Ignasi | contribution=The Sun and stars as the primary energy input in planetary atmospheres | title=Solar and Stellar Variability: Impact on Earth and Planets, Proceedings of the International Astronomical Union, IAU Symposium  | volume=264 | pages=3–18 |date=February 2010 | doi=10.1017/S1743921309992298 | bibcode=2010IAUS..264....3R |arxiv = 0911.4872 | s2cid=119107400 | contribution-url=https://www.cambridge.org/core/services/aop-cambridge-core/content/view/293C0314C44A1A4AAF8175A3C288B50B/S1743921309992298a.pdf/sun_and_stars_as_the_primary_energy_input_in_planetary_atmospheres.pdf }}</ref>]]
The '''solar luminosity''' ('''{{Solar luminosity}}''') is a unit of [[radiant flux]] ([[Power (physics)|power]] emitted in the form of [[photon]]s) conventionally used by [[astronomer]]s to measure the [[luminosity]] of [[star]]s, [[galaxy|galaxies]] and other celestial objects in terms of the output of the [[Sun]].

One nominal solar [[luminosity]] is defined by the [[International Astronomical Union]] to be {{val|3.828|e=26|ul=W}}.<ref>{{cite web |url=https://www.iau.org/static/resolutions/IAU2015_English.pdf|title=Resolution B3 on recommended nominal conversion constants for selected solar and planetary properties|publisher=International Astronomical Union|date=2015|access-date= 5 June 2018}}</ref>  This corresponds almost exactly to a [[bolometric magnitude|bolometric absolute magnitude]] of +4.74.

The Sun is a weakly [[variable star]], and its actual luminosity therefore [[Solar variation|fluctuates]].<ref>{{Cite journal | last1 = Vieira | first1 = L. E. A. | last2 = Norton | first2 = A. | last3 = Dudok De Wit | first3 = T. | last4 = Kretzschmar | first4 = M. | last5 = Schmidt | first5 = G. A. | last6 = Cheung | first6 = M. C. M. | doi = 10.1029/2012GL052950 | title = How the inclination of Earth's orbit affects incoming solar irradiance | journal = Geophysical Research Letters | volume = 39 | issue = 16 | page = L16104 (8 pp.) | year = 2012 | bibcode=2012GeoRL..3916104V | url = https://pubs.giss.nasa.gov/docs/2012/2012_Vieira_vi06000k.pdf | id = [https://hal-insu.archives-ouvertes.fr/insu-01179873 insu-01179873] | doi-access = free }}</ref> The major fluctuation is the eleven-year [[solar cycle]] (sunspot cycle) that causes a quasi-periodic variation of about ±0.1%. Other variations over the last 200–300 years are thought to be much smaller than this.<ref name="Noed">{{cite journal |last=Noerdlinger |first=Peter D. |arxiv=0801.3807 |title = Solar Mass Loss, the Astronomical Unit, and the Scale of the Solar System |journal = Celestial Mechanics and Dynamical Astronomy |bibcode=2008arXiv0801.3807N |volume=801 |date=2008 |page=3807}}</ref>