Hi Folks,
We've been asking users to NOT use AO-91 when it is in eclipse. I've gotten some questions about this, which is great. Here is a bit of info that is more operational than analytical!
The best way to know if a satellite is in eclipse is to use software. I use SatPC32 and it shows when a satellite is in sunlight and when it's in the dark (eclipse). Remember, you can download a demo version limited only by having to enter your info/lat/long each time you start the program. Surely many other programs indicate eclipse/sunlight as well, but since I don't use them, I can't say for sure. Maybe there is a list somewhere, or maybe we can build a list here! (PREDICT does, Gpredict probably does, as I would guess Macdoppler as well?) There is also a program called ILLUM by DK3WN that is really superb for long term calculations. Others can chime in (please!) if you know of a program that shows sunlight/eclipse for a satellite.
This is far from perfect, but a good "rule of thumb" for AO-91--if you're in the continental US/Hawaii, and if it's dark outside, the satellite is in eclipse so please don't use it during evening passes. When it's daytime/daylight at your QTH, then AO-91 is in sunlight and it's OK to use. This appears to hold true for AO-91 pretty much of the year due to its orbit. If you live at a very northern latitude, things get more interesting ;)
If a satellite seems to linger along the terminator line (day/night line), you're really going to need software to tell you!
Thanks for your help and cooperation.
Hope that helps...
73,