Re: ISS Misses Moon - not by much!

From: Tom Wagner (
Date: Tue Jun 05 2001 - 10:46:35 PDT

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    What about seeing a more constant source of light, like the sun reflected
    off any of the satellites that are let's say magnitude 4 or brighter. I
    realize that earthshine is not always the same brightness and that past a
    few days it's not even noticeable, but it wouldn't it be much more likely to
    see this than trying to see a flare crossing the moon's disc?
    We could limit the moon's phase from whatever it is when the moon is 15
    degrees above the horizon (another variable I'm sure) to 1st quarter then
    choose the conjugate occurrence at the other end of the lit cycle. At 15
    degrees it would have to occur right then. At 1st quarter it would have more
    time to occur.
    Any estimates?
    ----- Original Message -----
    From: "Bruno Tilgner" <>
    To: <>
    Sent: Tuesday, June 05, 2001 5:19 AM
    Subject: Re: ISS Misses Moon - not by much!
    > 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
    > brighter.
    > 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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