Re: Has anyone seen daylight Iridium flares?

Doyle J. Groves (deej@deej.com)
Sat, 18 Apr 1998 12:50:53 -0500

At 01:14 AM 4/18/98 , you wrote:

>So naturally I am begning to wonder if the predictions are working for
>other observers. Any luck out there? What technique did you use? 

Just last evening, for the first time, I witnessed a daytime flare.  The
sun was still 5.3 degrees above the horizon.  The predicted mag was -8.2,
and I can't say definitively if it was achieved, but it was significantly
brighter than the typical 1x Venus at the same daylight level.

You outlined a very solid approach for finding a proper look angle from
your location (find ref stars the night before, landmark the spot with
terrestrial objects, etc.).  I only discovered the flare prediction earlier
in the day, without a night to find some ref stars as you suggest.

I was lucky in that the Az/El look angle was in "nice round numbers" that I
could estimate, those being Az = about 180 (i.e. *south*) and El = about 60
(i.e. two-thirds of the way up).    I feel I was within about 5 degrees in
my initial target scan area.

Of course, timing is everything, and with OIG elsets only a few hours old,
and with my freshly calibrated stopwatch (UT), the few-second window in
which the mag was to be -4 or better was *right on time*!  This was for
Iridium 22 and centered around 18:52:51 local CDT near Indianapolis, IN.

To top if off, a mag -6.2 came through about 110 minutes later (Iridium 28,
20:37:51 CDT).  Easier to pre-find with ref stars; about 20 to 25 seconds
in duration since night seeing was now in effect; indescribably bright
relative to the earlier one, even though it was *only* mag -6.2!  These
were great back-to-back events to compare and contrast.

Thanks to Rob Matson and others for the great software tools that are
enabling witnessing the spectacular events like I saw last evening.


Doyle Groves
Noblesville, IN
40.09 N, 86.06 W


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