Editing Luminosity (section)

{{Short description|Measurement of radiant electromagnetic power emitted by an object}}
{{Other uses}}
{{Use dmy dates|date=October 2019}}
[[File:The Sun in white light.jpg|thumb|The [[Sun]] has an intrinsic luminosity of {{val|3.83|e=26|u=[[watt]]s}}. In astronomy, this amount is equal to one [[solar luminosity]], represented by the symbol ''L''<sub>⊙</sub>. A star with four times the radiative power of the Sun has a luminosity of {{val|4|u=''L''<sub>⊙</sub>}}.]]
'''Luminosity''' is an absolute measure of radiated [[electromagnetic radiation|electromagnetic energy]] per unit time, and is synonymous with the [[radiant power]] emitted by a light-emitting object.<ref>{{Cite news|url=https://www.britannica.com/science/luminosity|title=Luminosity {{!}} astronomy|work=Encyclopedia Britannica|access-date=24 June 2018|language=en}}</ref><ref>{{Cite web|url=https://en.mimi.hu/astronomy/luminosity.html|title=* Luminosity (Astronomy) - Definition, meaning - Online Encyclopedia|website=en.mimi.hu|access-date=24 June 2018}}</ref> In [[astronomy]], luminosity is the total amount of electromagnetic [[energy]] emitted per unit of [[time]] by a [[star]], [[galaxy]], or other [[astronomical object|astronomical objects]].<ref name=Hopkins1980>{{cite book |last=Hopkins |first=Jeanne |title=Glossary of Astronomy and Astrophysics |edition=2nd |publisher=[[The University of Chicago Press]] |date=1980 |isbn=978-0-226-35171-1}}</ref><ref>{{cite book |last1=Morison |first1=Ian |title=Introduction to Astronomy and Cosmology |date=2013 |publisher=Wiley |isbn=978-1-118-68152-7|url=https://books.google.com/books?id=Fh_yo8Jv7t8C&pg=PT193|page=193}}</ref>

In [[SI]] units, luminosity is measured in [[joules]] per second, or [[watt]]s. In astronomy, values for luminosity are often given in the terms of the [[Solar luminosity|luminosity of the Sun]], ''L''<sub>⊙</sub>. Luminosity can also be given in terms of the astronomical [[Magnitude (astronomy)|magnitude]] system: the [[Absolute magnitude#Bolometric magnitude|absolute bolometric magnitude]] (''M''<sub>bol</sub>) of an object is a logarithmic measure of its total energy emission rate, while [[absolute magnitude]] is a logarithmic measure of the luminosity within some specific [[wavelength]] range or [[Passband|filter band]].

In contrast, the term ''brightness'' in astronomy is generally used to refer to an object's apparent brightness: that is, how bright an object appears to an observer. Apparent brightness depends on both the luminosity of the object and the distance between the object and observer, and also on any [[Extinction (astronomy)|absorption]] of light along the path from object to observer. [[Apparent magnitude]] is a logarithmic measure of apparent brightness. The distance determined by luminosity measures can be somewhat ambiguous, and is thus sometimes called the [[luminosity distance]].