Re: Do Not Work AO-91 in Elipse!

Clint Bradford

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...


Mark L. Hammond [N8MH]
AMSAT Director and Command Station


Sent via AMSAT-BB(a) AMSAT-NA makes this open forum available
to all interested persons worldwide without requiring membership. Opinions expressed
are solely those of the author, and do not reflect the official views of AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite program!

View archives of this mailing list at
To unsubscribe send an email to amsat-bb-leave(a)
Manage all of your AMSAT-NA mailing list preferences at

Join to automatically receive all group messages.