QUOTE (ngunn @ May 10 2009, 02:29 PM)
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Some very rough calculations tell me that, seen from Titan, Hyperion and Iapetus at their best are only about as bright as brightish stars so I don't think they are responsible.
I don't know what the geometry is here (i.e. whether any satellite is particularly well-placed to
illuminate the nightside) but in fact the satellites are quite bright - I worked out how bright they
would be once for astronavigation of balloons etc on Titan. If my calculations are correct, the
sources are as follows (so perhaps are bright enough for the observed surface brightness..)
Object Mag1 Size2 Comment
Saturn -14.2 5.5o 11x bigger, 10x brighter than Moon seen from Earth
*Tethys -5.4 3.9’ ~10x brighter than Venus from Earth
*Dione -5.7 4.7’
*Rhea -6.2 7.9’ 1/3 size of Moon seen from Earth
Hyperion -3 2.3’
Iapetus -2 2.0’ as bright as Jupiter seen from Earth
Earth -4.5 (tiny)
Jupiter -0.4 0.7’
*Orbit inside Titan’s, so visibility not very different from Saturn’s
1 Magnitude under best geometry. Brightness~10(-1.0*magnitude/2.5)
2 Largest apparent size in arcminutes, except Saturn