Editing Reflection nebula (section)

==Luminosity law==
[[File:Cosmic dust clouds in reflection nebula Messier 78.jpg|thumb|200 px|Cosmic dust clouds in [[Messier 78]].<ref>{{cite news|title=Sifting through Dust near Orion's Belt|url=http://www.eso.org/public/news/eso1219/|access-date=2 May 2012|newspaper=ESO Press Release}}</ref> ]]
In 1922, [[Edwin Hubble]] published the result of his investigations on [[bright nebula]]e. One part of this work is the Hubble luminosity law for reflection nebulae, which makes a relationship between the [[angular size]] (''R'') of the nebula and the [[apparent magnitude]] (''m'') of the associated star:
{{block indent|1={{math|1=5 [[logarithm|log]]({{var|R}}) = &minus;{{var|m}} + {{var|k}}}}}}
where {{mvar|k}} is a constant that depends on the sensitivity of the measurement.