Re: Brightness of GRACE Satellites

From: Bram Dorreman (
Date: Sun Oct 29 2006 - 14:49:27 EST

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    Gerhard HOLTKAMP worote:
    . . .with the pair of GRACE satellites (2002-012A and 2002-012B).
    > What I find strange is that they fluctuate strongly in brightness (even
    > during the 20 sec exposures). The visual report (they were also observed
    > through binoculars) mentioned the leading satellite fluctuating between mag
    > 5
    > and less than mag 8 (then disappearing) and the trailing satellite was
    > between mag 3 and mag 5.>
    My experience until now:
    Most transits of GRACE Satellites result in steady appearing satellites.
    Sometimes the conditions are suitable to let the two spacecraft show
    one flare. I did not analyse those special cases. But I presume that
    there might be a connection: GRACE's azimuth equals Sun's azimuth. I
    did not prove this yet.
    When one speaks about variable satellites, what does one mean?
    If there is one and sometimes are two increases in brightness for a
    short time within a transit, I regard these satellites as steady and
    they have flared. If there is a more or less periodicity in
    brighntness fluctuations I suspect the satellite to be rotating one
    way or another.
    Therefore my question: how many brightness variations were actually seen?
    Bram Dorreman
    COSPAR 4160
    51° 16' 45.5" N 5° 28' 36.6" E (WGS84) 35 m
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