the point is, that planets are much more than mapped spheres and an atmosphere is more than a glow. and that's why real time rendered planets(those i've seen) don't look very realistic.
and of course my planets are sexed up, because it looks much more interesting.
...it eats up a lot of memory
very true *g*
my planets are build of 3 spheres. one for the surface, one for the clouds and one for the atmosphere.
the surface sphere is mapped usually by a diffuse map(color) a bump map(very very little bump, in most renderings of this resoluttion not noticable), and a self illumination map to light the dark side. the diffuse maps are painted from photos or generated procedural.
the cloud sphere is very similar to the surface sphere. but it's slightly larger and it's material has an additional opacity map.
the atmosphere is then mapped using falloff maps.(in this case, the falloff maps make the material only appear on the light side)
maybe it helps if i show you the material tree
the planets itself don't have nightlights... i rendered them seperate on a sphere as big as the surface with an alpha map showing only the lights... this gets then simply layered over the planet frames.
to get more the look of a planet i had to change the shading to oren-nayar-blinn and chang the contrast settings of my light source.
if you could do all this stuff in realtime, it would look like my planets. i'm sure it will be possible in future, but not today ;)