Re: Daytime Iridium Flares - plus more (fwd)

Bart De Pontieu (
Mon, 9 Feb 1998 13:52:42 +0100 (MET)

The cds-machine was down this morning, hence this manual forwarding of a
message sent by Jake Rees this morning.

-- Bart

---------- Forwarded message ----------
Date: Mon, 9 Feb 1998 04:54:51 EST
Subject: Re: Daytime Iridium Flares - plus more
Resent-Date: Mon, 9 Feb 1998 04:54:51 EST

Don Gardner wrote:

<< Next Friday (2/13) at 4:43pm local time (21:43 UT) there is a predicted -8
 flare for my work location (39.1861N  76.6869W  34mASL).  It will be nearly
 vertical (89 deg el).  At 4:43pm yesterday I noted the brightness of the sky.
 Twlight isn't until about 6:10pm.
 A question for the people on the list who have seen daytime flares:  How long
 are they visible?  The evening and twilight flares that I've observed are
 typically visible at 1x for as long as 15 secs.   I'm hoping for about 5
 seconds for the daylight flare. >>

I've seen two daylight Iridium flares.  The first one 31 Oct. 97 @ 14:31:17
was predicted -6.1 at az. 009 elev. 72.  The sun was about 3 degrees above
the horizon.  I saw it long enough to say "there it is" and it was gone.
one-half sec., so I assume that only the max. peak was seen or maybe my 
eyes just didn't focus on it soon enough to see it longer.  This was with the
unaided eye and without an instrument of some kind, to tell me exactly where 
to look.   I was just trying to keep my eyes quickly scanning around the area
that I thought was az. 009 elev. 72.

You have a definite advantage with yours, weather permitting.  Being basically
straight overhead and magnitude -8, my guess is to agree that you might see it
for perhaps as much as 5 sec.  Do you suppose you can get away with lying
in a chaise lounge looking straight up for a few minutes without raising too
many eyebrows?  It might help to be at a location where the sun is blocked 
by a building or tree.  Hope the weather cooperates and please report if you
see it or even if not.

My second daylight Iridium flare was UTC date 22 Nov. 97 @ 00:40:19 UTC.
Predicted to be magnitude -4.1 by Iridflar, it was to appear about 8 degrees
west of Venus.  The sun was 0.7 degrees above the horizon.  A few minutes
before the event, I had stepped out to see if Venus could be spotted naked
eye.  Trying briefly, I didn't see it.  Since Venus is similar magnitude, I 
decided the best thing was to use binoculars (7x35).  Again, not sure exactly
where it was to appear, I used dead reckoning to choose where to look and
made a quick scanning motion around that area.  It appeared right on time
first seen in the right side of my field of view through the binoculars and I
reported the duration of visibility to be about 2 sec.  It might have been 3.

I want to attempt to see more daylight Iridium flares.  Just need to get my
personal schedule and the weather to work together and remember to run
Iridflar to predict them.  I did try one a couple of months ago; even drove to
the max. flare latitude and longitude; don't remember what the mag. was
supposed to be, but I saw nothing.  The sky was hazy and the flare was
in the same half of the sky as the sun.  A lot of the daylight flares that 
I've noticed predicted by Iridflar seem to be in the same quadrant of sky 
as the sun, which would seem to be a distinct disadvantage.

I believe someone recently expressed on SeeSat his happiness that
Iridiums flare.  I agree, as it make the hobby much more interesting.
I still wonder if the designers didn't realize that they would flare brightly.
How could they NOT realize it with each one having three antennas with
mirror-like surfaces pointing towards the earth!  Maybe they did realize
it but that fact just had no bearing on what they were trying to accomplish.
As for interference with professional astronomical studies, the concensus
on SeeSat with a few professional astronomers involved in the discussion,
seemed to be that the flares were no big problem.  Maybe I ramble too

On another subject, from ISIR Newsline Digest:
<< Feb 13  The first four Globalstar spacecraft are scheduled to
        be launched aboard a Boeing Delta II rocket at 13:22
        UTC from Cape Canaveral Air Station in Florida.  >>

I watched the satellite TV feed of the launch attempt Sun. AM (scubbed). 
I gather that the Boeing Delta 2 launch team, who must fly back and forth
between Florida and California to launch Delta 2's, needed to travel to 
California to attempt to launch the next Delta 2/Iridium from Vandenberg 
AFB the morning of Feb. 11 @ 14:37 UTC.  They're a busy group lately.

Jake Rees
Burbank, California
(34.164 N, 118.341 W) 190 m.