# Re: ISS Misses Moon - not by much!

From: Bruno Tilgner (Bruno_Tilgner@compuserve.com)
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

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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