View source for Luminosity

[[File:Phot-27e-07.jpg|thumb|230px|right|Image of galaxy [[NGC 4945]]. It shows the huge luminosity of the central star clusters, suggesting there are 10 to 100 supergiant stars in each of these, packed into regions just a few [[parsecs]] across.]]

'''Luminosity''' is the amount of power given off by an [[astronomical object]].

[[Star]]s and other objects emit energy in the form of [[radiation]]. It is [[Measurement|measure]]<nowiki/>d in [[joules]] per second, which are equal to [[watt]]s. A watt is one unit of [[Power (physics)|power]]. Just as a [[light bulb]] is measured in watts, the [[Sun]] can also be measured in watts. The sun gives off {{val|3.846|e=26|u=[[Watt|W]]}}. This amount of power is known as 1 sol, the symbol for which is <math>L_\odot</math>.  

There are other ways to describe luminosity. The most common is [[apparent magnitude]], which is how bright an object looks to an observer on [[Earth]]. It only applies to light, that is, [[Visible light|visible wavelengths]]. Apparent magnitude is contrasted with [[absolute magnitude]], which is an object's ''intrinsic brightness'' at visible wavelengths, irrespective of distance.  The apparent magnitude is the less, for objects more than 32.6 light years away.

When talking about the total power output across [[Electromagnetic spectrum|all wavelengths]], that is called [[bolometric magnitude]].  


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== Luminosity Media ==
<gallery widths='160px' heights='100%' mode='traditional' caption=''>
File:The Sun in white light.jpg|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''⊙. A star with four times the radiative power of the Sun has a luminosity of {{val|4|u=''L''⊙}}.

File:Inverse square law.svg|Point source ''S'' is radiating light equally in all directions. The amount passing through an area ''A'' varies with the distance of the surface from the light.
</gallery>
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[[Category:Laws of physics]]