Re: double flash for Iridium 75?

From: Bjorn Gimle (b_gimle@algonet.se)
Date: Wed Jun 05 2002 - 09:53:29 EDT


Assuming you are on lat.40N, and the time of your obs was before sunset on
June 03 local time,
I used IridFlar to see when and where members of the same orbital plane
would flare, then adjusted the longitude to compensate for the time
difference between Ir 75 and the one I found.

This gives that you could have been at 95.30 deg. W and seen Ir 75 at
1:12:38 UTC, followed by Ir 21 (at the "same" spot) 22 seconds later.

Ir 75 would also flare n * 1:40:28 later (earlier) and 25.20 deg. W (E)

Times and longitudes will be slightly altered by setting latitude correctly.

Ir 21 is faster by about 85 seconds/orbit, so its flare would be 34 km E of
Ir 75's on the following orbit already, and not seen in daytime. (Near -95.3
it was just 2.5 km E)

Prediction for +40/-95.3 (several columns removed to fit mail):

                           Iridium      Solar             Maximum Flare
Ir# S    Date     UTC Time  Azm El  N Azm  Elev M  Mag Latitude Longitude
-------------------------------------------------------------------------
18    2002- 6- 4  0:33:50.0 317 49  A 290  11.6 L  4.8  38.7505  -95.3475
18    2002- 6- 4  0:34:09.3 325 44  A 290  11.6 L -5.1  39.9728  -95.2289
18    2002- 6- 4  0:34:30.0 332 40  A 290  11.5 L  4.7  41.2821  -95.0926

75    2002- 6- 4  1:12:20.0 039 80  D 295   4.9 R  4.5  41.0451  -95.2847
75    2002- 6- 4  1:12:37.9 109 83  D 295   4.8 R -8.4  39.9986  -95.3152
75    2002- 6- 4  1:13:00.0 154 74  D 296   4.8 R  5.0  38.7077  -95.3547

21  ? 2002- 6- 4  1:12:50.0 060 83  D 296   4.8 R  2.7  40.6030  -95.2705
21  ? 2002- 6- 4  1:13:00.2 110 83  D 296   4.8 R -8.6  39.9969  -95.2861
21  ? 2002- 6- 4  1:13:20.0 154 74  D 296   4.7 R  4.8  38.8211  -95.3176

----- Original Message -----
From: "Sue Wheatley" <mswheatley@txucom.net>
To: <SeeSat-L@satobs.org>
Sent: Tuesday, June 04, 2002 8:06 PM
Subject: double flash for Iridium 75?


> Yesterday Heavens-Above indicated a daytime flare of Iridium 75 at my
site.
> Indeed it appeared 77 degrees alt and 111 degrees azimuth, faded, and then
> re-brightened at about 60 degrees alt and 130 azim.  (Those last two
numbers
> are pretty shaky.)
>     I've watched many Iridiums during darkness, and they brighten--dim,
and
> that is it. This is my first daytime flare.  Is this on-off phenomenon
> common for daytime flares?
> --sue
>
> -----------------------------------------------------------------
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>

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