The Hubble–Reynolds law models the surface brightness of elliptical galaxies as Where
is the radius at which the surface brightness is diminished by a factor of 1/4.
It is asymptotically similar to the De Vaucouleurs' law which is a special case of the Sersic profile for elliptical galaxies.
[1] The law is named for the astronomers Edwin Hubble and John Henry Reynolds.
It was later re-derived by Hubble in 1930[3] specifically in observations of elliptical galaxies.