shadow accuracy

Walter Nissen (dk058@cleveland.Freenet.Edu)
Sat, 23 Dec 1995 13:19:28 -0500

Bj"orn Gimle writes: 
> I noticed large differences when I compared TrakSat, QuickSat, 
> SkyMap, SeeSat (and possibly ViewSat) with photographs I made 
> of a high Cosmos rocket, a shuttle, UARS and a few visual obs. 
> when entering shadow. I sent my data to Rob Matson, and with 
> his modifications I consider SkyMap very reliable now. 
In my experience, QuickSat is highly reliable.  Mir (very bright, mag 0 to 
-2) seems to disappear, by actual measurement of the time and comparison 
to an interpolation of the nearest, best elsets available (usually from 
OIG), when its SHD parameter is about 10 to 16 km.  Faint stuff (mag 4 to 
6) seems to disappear when SHD is about 30.  I believe the latest versions 
of QS incorporate a heuristic which closely approximates my experience. 
In one case I checked, TS was 3 minutes out of whack; though typically 
considerably less. 
Walter Nissen          
Better to extinguish one candle than to curse the light.