Re: Multiple Iridium Flares

Bjoern Gimle (
Fri, 24 Oct 1997 10:58:08 +0100

14 hours ago I sent this from my home address. If it turns up duplicated,
I apologize:

To: SeeSat-L (no attachment), Ron Lee <>
From: (Bjoern Gimle)
Subject: Re: Multiple Iridium Flares
Attachments: H:\RONLEE.TXT;

>PS.   From my location, flares are minimal.   Perhaps due to orbital
>placement of the Iridiums.   We need more up there to observe!
I agree with the latter sentence. I don't think you're worse off.

There is very little pattern to the Iridium tracks. They do repeat
in time on 43 orbits = 3.0000 days. But the orbit has precessed, and
it takes 18 days (257 orbits) for a track to repeat within 0.2 degrees
of longitude, but in that time the Sun position has shifted so much
that there is no similarity in flaring.

The new launches at MM=15.03 have a day-to-day shift of about 0.6 deg.W

Ron has a predicted .9 degree flare tonight by Ir 17, and about six
more negative-magnitude flares in the mornings of the coming fortnight.

I am favo(u)red by the tracks being denser E-W by a factor of 1/cos(lat),
and because of inclinitation, which combine as 1/sqrt(cos^2(lat)-cos^2(i))
This is the effect on the number of high passes. The factor 1/cos(lat)
also affects the number of twilight passes (approximately - I have terrible
summers for satellite watching, and most of winter twilight during work hours)

The factors mentioned are 
  lat=   34.6100	          1.2186	          1.2150
  lat=   59.2200	          1.9690	          1.9541


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