Editing Effective temperature (section)

== Star ==

[[File:EffectiveTemperature 300dpi e.png|thumb|250px|The effective temperature of the [[Sun]] (5778 [[kelvin]]s) is the temperature a black body of the same size must have to yield the same total emissive power.]]

The effective temperature of a [[star]] is the temperature of a [[black body]] with the same luminosity per ''surface area'' ({{math|{{mathcal|F}}<sub>Bol</sub>}}) as the star and is defined according to the [[Stefan–Boltzmann law]] {{math|{{mathcal|F}}<sub>Bol</sub> {{=}} ''σT''<sub>eff</sub><sup>4</sup>}}. Notice that the total ([[Absolute magnitude|bolometric]]) luminosity of a star is then {{math|''L'' {{=}} 4π''R''<sup>2</sup>''σT''<sub>eff</sub><sup>4</sup>}}, where {{math|''R''}} is the [[stellar radius]].<ref>{{cite book
 | first=Roger John | last=Tayler | date=1994
 | title=The Stars: Their Structure and Evolution
 | publisher=[[Cambridge University Press]] | isbn=0-521-45885-4
 | page=16 }}</ref> The definition of the stellar radius is obviously not straightforward. More rigorously the effective temperature corresponds to the temperature at the radius that is defined by a certain value of the [[Rosseland optical depth]] (usually 1) within the [[stellar atmosphere]].<ref name="Bohm">{{Cite book|title=Introduction to Stellar Astrophysics, Volume 3, Stellar structure and evolution|first=Erika|last=Böhm-Vitense|year=1992|page=14|publisher=[[Cambridge University Press]]|bibcode=1992isa..book.....B}}</ref><ref>{{cite journal|title=The parameters R and Teff in stellar models and observations|last=Baschek|bibcode=1991A&A...246..374B
|journal = Astronomy and Astrophysics
| volume = 246 |issue=  2 |date= June 1991 |pages= 374–382}}</ref> The effective temperature and the bolometric luminosity are the two fundamental physical parameters needed to place a star on the [[Hertzsprung–Russell diagram]]. Both effective temperature and bolometric luminosity depend on the chemical composition of a star.

The effective temperature of the Sun is around {{val|fmt=commas|5,778|ul=K}}.<ref name="Ref_">{{Cite book |editor-last=Lide |editor-first=David R. |section=Properties of the Solar System |publisher=[[CRC Press]] |title=CRC Handbook of Chemistry and Physics |section-url=https://books.google.com/books?id=WDll8hA006AC&pg=SA14-PA2 |edition=85th |page=[https://archive.org/details/crchandbookofche81lide/page/14 14<nowiki>-</nowiki>2] |date=2004 |isbn=9780849304859 |url-access=registration |url=https://archive.org/details/crchandbookofche81lide/page/14 }}</ref><ref name="Jones2004">{{cite book|title=Life in the Solar System and Beyond|first=Barrie William|last=Jones|page=7|publisher = [[Springer Science+Business Media|Springer]]|date=2004|isbn=1-85233-101-1| url=https://books.google.com/books?id=MmsWioMDiN8C&pg=PA7}}</ref>
The nominal value defined by the [[International Astronomical Union]] for use as a unit of measure of temperature is {{val|fmt=commas|5,772|0.8|u=K}}.<ref>{{Cite journal|bibcode = 2016AJ....152...41P|title = Nominal Values for Selected Solar and Planetary Quantities: IAU 2015 Resolution B3|last1 = Prša|first1 = Andrej|last2 = Harmanec|first2 = Petr|last3 = Torres|first3 = Guillermo|last4 = Mamajek|first4 = Eric|last5 = Asplund|first5 = Martin|last6 = Capitaine|first6 = Nicole|last7 = Christensen-Dalsgaard|first7 = Jørgen|last8 = Depagne|first8 = Éric|last9 = Haberreiter|first9 = Margit|last10 = Hekker|first10 = Saskia|last11 = Hilton|first11 = James|last12 = Kopp|first12 = Greg|last13 = Kostov|first13 = Veselin|last14 = Kurtz|first14 = Donald W.|last15 = Laskar|first15 = Jacques|last16 = Mason|first16 = Brian D.|last17 = Milone|first17 = Eugene F.|last18 = Montgomery|first18 = Michele|last19 = Richards|first19 = Mercedes|last20 = Schmutz|first20 = Werner|last21 = Schou|first21 = Jesper|last22 = Stewart|first22 = Susan G.|journal = The Astronomical Journal|year = 2016|volume = 152|issue = 2|page = 41|doi = 10.3847/0004-6256/152/2/41|arxiv = 1605.09788|hdl = 1885/108637|s2cid = 55319250 | doi-access=free }}</ref>
Stars have a decreasing temperature gradient, going from their central core up to the atmosphere. The "core temperature" of the Sun—the temperature at the centre of the Sun where nuclear reactions take place—is estimated to be 15,000,000&nbsp;K.

The [[color index]] of a star indicates its temperature from the very cool—by stellar standards—red M stars that radiate heavily in the [[infrared]] to the very hot blue O stars that radiate largely in the [[ultraviolet]]. Various colour-effective temperature relations exist in the literature. Their relations also have smaller dependencies on other stellar parameters, such as the stellar metallicity and surface gravity.<ref>{{cite journal |last1=Casagrande |first1=Luca |title=The GALAH survey: effective temperature calibration from the InfraRed Flux Method in the Gaia system |journal=MNRAS |year=2021 |volume=507 |issue=2 |pages=2684–2696 |doi=10.1093/mnras/stab2304 |doi-access=free |arxiv=2011.02517 |bibcode=2021MNRAS.507.2684C }}</ref> The effective temperature of a star indicates the amount of heat that the star radiates per unit of surface area. From the hottest surfaces to the coolest is the sequence of [[stellar classification]]s known as O, B, A, F, G, K, M.

A red star could be a tiny [[red dwarf]], a star of feeble energy production and a small surface or a bloated giant or even [[supergiant]] star such as [[Antares]] or [[Betelgeuse]], either of which generates far greater energy but passes it through a surface so large that the star radiates little per unit of surface area. A star near the middle of the spectrum, such as the modest [[Sun]] or the giant [[Capella (star)|Capella]] radiates more energy per unit of surface area than the feeble red dwarf stars or the bloated supergiants, but much less than such a white or blue star as [[Vega]] or [[Rigel]].