Re: significantly different predictions by different programs

From: Björn Gimle (
Date: Tue Oct 31 2006 - 06:37:28 EST

  • Next message: Tony Beresford: "observations from 8597 oct 31"

    For Rob Matson's SkyMap program, this is an optional feature
    for the 'Stereographic' (AltAz) projection only, labelled
    'Horizontal' in the menu, 'Hor' below the map, so the user
    is aware of these 'problems'. (Default is 'Equatorial', 'Equ'
    below the map). The stars (and planets and asteroids!) are
    plotted in correct AltAz for a selected 'Map Date and Time',
    independent of the satellite pass times (which in turn can
    be selected individually if desired)
    Horizontal mode can be very useful when you want to select
    parts of a long- duration track sufficiently high, and most
    important free of any terrain and housing obstacles (which
    can also be drawn by SkyMap!)
    The grid is AltAz in both stereographic modes, RA/Dec in
    Polar and Rectangular modes, but in all modes you can
    inquire (? or q) for the star close to the cursor.
    (In the horizontal mode you could then get an approximate
    RA/Dec by adding the siderial time difference between map
    time and track time for a star close to the track.)
    Sample prediction maps for a pass by ETS-6 in the different
    modes are available on request.
    ----- Original Message -----
    > >It has come to my attention that among the programs being used for
    > >predictions, there are some significantly differing results for
    > >at least some objects.  A specific case is ETS 6 (94-56A, 23230).
    > >
    > When I ran Heavensat in the "passes prediction" mode, the output
    > was the entire 14 hours that ETS 6 was above my horizon (even though
    > the duration was set to 20 minutes).  The [***] was around the maximum
    > altitude of the pass - alt 62, azi 153, time 12:22.  So this was 10
    > hours after the 20 minute "duration" of the prediction.  I could
    > zoom in on the 02:00 part of the trajectory and the alt/azi was
    > correct, but the 6th magnitude star did not appear.  It seems that
    > the stars are in their proper places for 12:22 UT, not 02:00 UT.
    > There are no RA and Dec labels on this display.  This is confusing.
    > So I can see how you could select a part of the trajectory that
    > was one or more hours off of the time of prediction and the stars
    > would not be in the right place for that part of the trajectory.
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