: Philip Chien <kc4yer@amsat.org> wrote: > >Is there a reasonably accurate formula for calculating the predicted >magnitude for a satellite? I suspect that it would have to include the >satellite's cross section area, albedo, percentage sunlit (usually = either 1 >or 0), and distance from observer. I would suspect that the same = formula >could be used to calculate the magnitude of the moon, planets, and any >other objects which shine by reflected sunlight. > Skymap uses mag =3D rm + 5*log(distance/1000 km) - = 2.5*log(1-cos(ph)) where rm is the reference magnitude at 1000 km half phase (ph=3D90 d) Quicksat uses the rm at full phase (ph=3D180 d), which needs to be reduced by about 0.7, (or 2.5*log((1-cos(ph)/2) for this formula. There is also a substantial term for atmospheric extinction in Quicksat for low elevations. I have an old note that rm is 6.0 - 2.5*log(Area*albedo), but those factors are rarely known for satellites, so empirical rm is preferred. If full moon is -12.8, it needs rm =3D -24.9, which gives an albedo of = 0.25! Half moon would be -12.0, and one day moon (ph=3D12 d) -7.8. Something does not quite right there. Bjoern