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aircraft vs. satellite




  Aha -- now I understand.  When I looked at the individual
"dots" in the trail, I found that their JD times differered
by a few minutes.  That's why I concluded they were due to a
satellite -- an aircraft would move more than 3 degrees in a
single minute.

   But, thanks to Nick's message, I understand -- all the 
points came from a single image, and were really made at
the same time ... but the TASS software _gave them times
which were several minutes apart_ (incorrectly).  
The software said, "Oh, here's a point source -- it must
be a star, and since it's at this _position_, it must have
gone through my field of view at this _time_."  For true
stars, position _is_ related to time.  But for airplane
trails, it's not.

  Okay, I get it now.

  Is this good or bad?  I think neither -- it's just the way
things work out.  From now on, if we see a trail of dots
which moves diagonally across a field, and the dots are each
a few minutes apart, we'll know it was probably an aircraft.

  And, has Nick points out, especially if there are several 
parallel tracks :-)

                               Michael