Re: ISS Misses Moon - not by much!

From: Bruno Tilgner (
Date: Tue Jun 05 2001 - 03:19:45 PDT

  • Next message: David Brierley: "DMB Obs June 4-5"

    Bjorn Gimle wrote:
    >Just find any flare within a few degrees of the Moon, and run
    >IridFlar for one location N and one S of yours.
    The best approach would then be to calculate all flares for a
    given location and see if it's in the vicinity of the Moon or
    not. I don't expect that to happen very frequently as the
    following statistical consideration shows:
    I am very demanding and want the flare to occur right on the
    Moon's disk (this was the original message). The Moon cuts a
    solid angle of 5.98E-5 steradian (sr) out of the sky. The full
    visible sky having 2*pi = 6.28 sr, the Moon is approximately
    1/100 000th of it.
    If we assume the Iridium flares to be evenly distributed over
    the sky, the interval between flares in front of the Moon is
    about 10^5 flares.
    I get about 5 flares of magnitude 0 or brighter per 24 hours,
    so the 10^5 flares will have occurred in 2E4 days or 57.5 years.
    Quite a long time to wait.
    The flares may be spread evenly across the sky, the Moon's
    positions are certainly not. At mid-northern latitudes it
    spends most of the time in the southern part of the sky, i.e.
    between azimuth 90 and 270 degrees. This will more than double
    the time I have to wait; so we are at the order of magnitude 
    of a century.
    This is of course just a ballpark number. In practice one would
    probably count only nighttime flares, but then one must also
    consider the number of hours the Moon is above the horizon by
    night. One could take flares dimmer than magnitude 0, although
    that should not change the picture significantly because I would
    have to move my position only by a little for the flare to get
    All in all, it seems a pretty hopeless situation for a single
    observer. If there were a hundred of them all over the world
    they might succeed within a year or so. 
    Am I too pessimistic ?
    Bruno Tilgner
    48.85N 2.02E UTC+2
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