Re: double flash for Iridium 75?

From: Willie Koorts (
Date: Wed Jun 05 2002 - 03:32:54 EDT

On Tue, 4 Jun 2002, Sue Wheatley wrote:

> 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?

Hi Sue

A while ago, I had a very similar experience.  Heavens-above also
predicted a daytime flare of Iridium 29 for my site (forgot the mag. now).

I decided to try and capture this on video and set up my automated mount
to the position predicted by heavens-above.  I roughly set the camcoder's
zoom to give a FOV of around 5 degrees (judged by viewing the moon) and
started recording about a minute or so before the predicted flash time.
The flash happened dead on time and was visible in the viewfinder and
smack-bang in the centre!

Since my attention was divided between trying to spot it naked eye as well
as making sure the video camera got it, I did not see the "secondary"
flash at the time.  However, when played back on TV afterwards, I noticed
an identical but dimmer flash a few seconds before Iridium 29, slightly
off to the right and a little higher.

I first thought its perhaps due to lens flare but it did not make sense
since the main flash only happened afterwards by which time the
"secondary" flash had almost faded completely.

I re-checked heavens-above but no such flash was predicted.  Only after
running the full IRIDIUM.TLE through IRIDFLARE did I discover that I saw
Iridium 90? - the question mark indicates that it is not officially
operational, hence not guaranteed to flash, hence not predicted by
heavens-above.  I suggest you try and do the same for your observation and
see if you did not also observe a spare Iridium.

                       Willie Koorts

       Cape Town,  Observatory   33d 56' 03"S   18d 28' 36"E   GMT + 2h
       Wellington, South Africa  33d 38' 56"S   19d 00' 52"E   GMT + 2h

       For - Amateur Astronomy - Telescope Making - Satellite Tracking -
                   Visit  ....

Unsubscribe from SeeSat-L by sending a message with 'unsubscribe'
in the SUBJECT to

This archive was generated by hypermail 2b29 : Tue Jun 25 2002 - 20:50:33 EDT