Re: question - brightness of 20638 (ROSAT) + introducing myself

From: Tony Beresford (
Date: Thu Jun 26 2003 - 08:36:12 EDT

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    At 18:40 26/06/03, Marco Langbroek wrote:
    >I have a question for this list. We received a 'fireball' report for June
    >24, 21:24 UTC from Alphen a/d Rijn, the Netherlands. After questioning the
    >eyewitness it became apparent that the object was so slow it must have been
    >a satellite. Indeed, the trajectory for satellite # 20638 (ROSAT) perfectly
    >matches the observation both in time and sky trajectory.
    >My question is, if anybody knows what brightness this satellite can attain
    >and if it might show flares of considerable brightness. This because the
    >observer states he saw it attain a magnitude of mag. -6 for a few seconds.
    >Anyone available to confirm this?
    welcome to Seesat-L. Marco. A perfect mirror surface at 1000Km range
    and of area 1 square meter gives a specular solar reflection
    of magnitude -7. If we assume the minimum range to ROSAT was 500Km,
    the brightness rises to -8.5. Solar panels are in general 12percent
    relective in the visible, so the brightness for 1 square meter
    drops to -6.2. I think you can see from the pictures that the
    solar panel area of rosat is at least 1 square meter. 
    If its not working, its orientation is unknown. In a lot
    of satellites solar panels are kept pointing at the sun, which
    means ground observers cant get sunglints. Iridiums are an exception
    because of operational need. Rob Matson's IRIDFLAR programme
    gives solar panel flare predictions as well as the MMA sunglints
    that HA predicts.
    Tony Beresford
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