Re: Decay

From: Alan Pickup (
Date: Wed Jan 26 2000 - 14:24:26 PST

  • Next message: Eberst: "JAN25.OBS" writes
    >In looking for satellite decays ( NOT the shuttle reentry!), what should I 
    >look for, so as not to mistake it for a meteor? Are they slower, do they last 
    >I once observed what I thought was a meteor,-- but it was slower than meteors 
    >ive confirmed. It had no trail, and crossed about 1/3 of the sky. 
    Yes, decaying satellites move much more slowly across the sky than your
    typical meteor and may be visible for 30-90 seconds during a transit.
    Very few meteors are this slow, though it is true that some meteoric
    fireballs appear to last much longer (several seconds) than most of the
    meteors you see regularly. Some of this may be because their luminous
    phases last longer because they penetrate more deeply into the
    A typical satellite reentry report often describes pieces breaking off
    the main body and continuing along the path while (usually) falling
    behind, so you get a train of several fireballs. Contrary to popular
    myth, decaying satellites (with only rare exceptions) are moving almost
    parallel with the ground and do not plunge steeply Earthwards, at least
    while still self-luminous. Of course, this does not mean that you will
    never see a decaying satellite moving almost straight down in your sky -
    for example, after it has just passed overhead. It does mean, though,
    that if several observations combine to suggest that the object was
    following a steep trajectory into the atmosphere, then it is most
    probably a meteor.
    Of course, another distinguishing feature is that you are extremely
    unlikely to encounter any satellite decaying from a strongly retrograde
    orbit. In other words, if the fireball or whatever has any pronounced
    weesterly motion (eg moving towards the SW, W or NW) then you can be
    confident that it is not a satellite decay.
     Alan Pickup | COSPAR 2707:  55d53m48.7s N  3d11m51.2s W   156m asl
     Edinburgh   | Tel: +44 (0)131 477 9144     Fax: +44 (0)870 0520750
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