Re: Zenit RB decay observed ?

From: Alan Pickup (
Date: Fri Oct 13 2000 - 13:55:28 PDT

  • Next message: Alan Pickup: "Decay watch: 2000 Oct 13"

    I agree with Harro that a more detailed account of this observation
    would be valuable - I am trying to get one.
    However, I am not sure that I agree fully with Harro's calculations.
    While I believe Harro is correct for an observer on the ground in
    Maseru, Lesotho, I suspect that he has not allowed for the 33,000 ft
    (not 11,000 ft) altitude of the observer. At such a height, the horizon
    is depressed below the horizontal by almost exactly 3 degrees - or put
    another way, the horizon is at an angular zenith distance of 93 degrees.
    At a range of 856 km and a height of 87 degrees, I get a zenith distance
    for the object of 88.7 degrees (observer at 33,000 ft), corresponding to
    an angle above the apparent horizon of 4.3 degrees. Given that the line
    of sight would be through relatively clean high-altitude air, it does
    not seem too surprising that the decay would be visible.
    Also, again because of the high vantage point, I suspect that it could
    have been in view for 3 minutes or more as it tracked southwards from
    the vicinity of Zumbo where Zambia, Zimbabwe and Mozambique meet on the
    Zambezi. This would lie in the NNE as seen from Maseru and the angular
    velocity would be surprisingly low at that range.
    Alan Pickup / COSPAR 2707:  55d53m48.7s N   3d11m51.2s W      156m asl
    Edinburgh  / SatEvo & elsets:
    Scotland  / Decay Watch:
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