Re: How inaccurate are predictions made months in advance?

Tony Beresford (
Sun, 26 Apr 1998 21:22:13 +0900

At 16:27 23/04/98 EDT, Jim Cook wrote:
>As an amateur astronomer, I volunteer at our local park system's public
>stargazing programs. Unfortunately, being a governmental body, they need to
>schedule their programs months in advance.  So when I'm asked by the park
>staff if I know of anything interesting going on in the sky, say, next August
>or September, as I was this morning, I don't usually check any of the
>satellite prediction tools I have simply because I know they may not be
>accurate that far down the road.  But it finally dawned on me that I really
>had little understanding of just what that error margin might be.
Just to test  a concrete example  , I recovered from my collection of old
elements provided by Muke McCant, a TLE for MIR epoch 97299
and compared its predictions with most current one off Alan Pickup's
select ( epoch 98115) using both Mike McCant's quicksat and TS Kelso's
TRAKSTAR for a pass on May 2, 1998 here in adelaide,sa(-34.97,138.7317E)
With Trakstar the two predictions only differed by 5 minutes! This of course
probably shows MIR hasnt had an orbital adjustment in Six months! Quicksat's
output differed by 30 minutes, but still good enough to decide if a 
pass was going to occur that night. Mike McCants has stated to me that
quicksat is not as accurate as trakstar when using old elements
Tony Beresford