Editing Luminosity (section)

== Measurement ==
When not qualified, the term "luminosity" means bolometric luminosity, which is measured either in the [[SI]] units, [[watt]]s, or in terms of [[solar luminosity|solar luminosities]] ({{solar luminosity}}).  A [[bolometer]] is the instrument used to measure [[radiant energy]] over a wide band by [[absorption (electromagnetic radiation)|absorption]] and measurement of heating.  A star also radiates [[neutrino]]s, which carry off some energy (about 2% in the case of the Sun), contributing to the star's total luminosity.<ref name="BAHCALL1">{{cite web |first=John |last=Bahcall |author-link=John N. Bahcall |url=http://www.sns.ias.edu/~jnb/SNviewgraphs/snviewgraphs.html |title=Solar Neutrino Viewgraphs |publisher=[[Institute for Advanced Study]] School of Natural Science |access-date=3 July 2012
}}</ref> The IAU has defined a nominal solar luminosity of {{val|3.828|e=26|u=W}} to promote publication of consistent and comparable values in units of the solar luminosity.<ref name=iau>{{cite arXiv |eprint=1510.07674|class=astro-ph.SR|title=IAU 2015 Resolution B3 on Recommended Nominal Conversion Constants for Selected Solar and Planetary Properties |last1=Mamajek|first1=E. E.|last2=Prsa|first2=A.|last3=Torres|first3=G.|last4=Harmanec|first4=P.|last5=Asplund|first5=M.|last6=Bennett|first6=P. D. |last7=Capitaine|first7=N. |last8=Christensen-Dalsgaard|first8=J.|last9=Depagne|first9=E.|last10=Folkner|first10=W. M.|last11=Haberreiter|first11=M. |last12=Hekker|first12=S. |last13=Hilton|first13=J. L.|last14=Kostov|first14=V.|last15=Kurtz|first15=D. W.|last16=Laskar|first16=J.|last17=Mason|first17=B. D.| last18=Milone|first18=E. F. |last19=Montgomery|first19=M. M.|last20=Richards|first20=M. T.|last21=Schou|first21=J.|last22=Stewart|first22=S. G.|year=2015}}</ref>

While bolometers do exist, they cannot be used to measure even the apparent brightness of a star because they are insufficiently sensitive across the [[electromagnetic spectrum]] and because most wavelengths do not reach the surface of the Earth.  In practice bolometric magnitudes are measured by taking measurements at certain wavelengths and constructing a model of the total spectrum that is most likely to match those measurements.  In some cases, the process of estimation is extreme, with luminosities being calculated when less than 1% of the energy output is observed, for example with a hot [[Wolf-Rayet star]] observed only in the infrared. Bolometric luminosities can also be calculated using a [[bolometric correction]] to a luminosity in a particular passband.<ref name=nieva>{{cite journal|bibcode=2013A&A...550A..26N| arxiv=1212.0928| title=Temperature, gravity, and bolometric correction scales for non-supergiant OB stars|journal=Astronomy & Astrophysics|volume=550|pages=A26|last1=Nieva|first1=M.-F|year=2013| doi=10.1051/0004-6361/201219677|s2cid=119275940}}</ref><ref name=buzzoni>{{cite journal|bibcode=2010MNRAS.403.1592B|arxiv=1002.1972|title=Bolometric correction and spectral energy distribution of cool stars in Galactic clusters|journal=Monthly Notices of the Royal Astronomical Society| volume=403|issue=3|pages=1592 |last1=Buzzoni|first1=A |last2=Patelli|first2=L|last3=Bellazzini|first3=M|last4=Pecci|first4=F. Fusi|last5=Oliva|first5=E| year=2010| doi=10.1111/j.1365-2966.2009.16223.x|doi-access=free |s2cid=119181086}}</ref>

The term luminosity is also used in relation to particular [[passband]]s such as a visual luminosity of [[k band (infrared)|K-band]] luminosity.<ref>{{Cite web|url=http://www.faculty.virginia.edu/ASTR5610/lectures/LECTURE2/lec2a.html|title=ASTR 5610, Majewski [SPRING 2016]. Lecture Notes|website=www.faculty.virginia.edu|access-date=3 February 2019|archive-date=24 April 2021|archive-url=https://web.archive.org/web/20210424171700/https://faculty.virginia.edu/ASTR5610/lectures/LECTURE2/lec2a.html|url-status=dead}}</ref> These are not generally luminosities in the strict sense of an absolute measure of radiated power, but absolute magnitudes defined for a given filter in a [[photometric system]].  Several different photometric systems exist.  Some such as the UBV or [[UBV photometric system|Johnson]] system are defined against photometric standard stars, while others such as the [[AB magnitude|AB system]] are defined in terms of a [[spectral flux density]].<ref name=delfosse>{{citation |bibcode=2000A&A...364..217D |display-authors=1 |last1=Delfosse |first1=Xavier |last2=Forveille |first2=Thierry |last3=Ségransan |first3=Damien |last4=Beuzit |first4=Jean-Luc |last5=Udry |first5=Stéphane |last6=Perrier |first6=Christian |last7=Mayor |first7=Michel |title=Accurate masses of very low mass stars. IV. Improved mass-luminosity relations |journal=Astronomy and Astrophysics |volume=364 |pages=217–224 |date=December 2000 |arxiv = astro-ph/0010586 }}</ref>