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 From: JRBURCA@aol.com To: SeeSat-L@cds.plasma.mpe-garching.mpg.de Subject: Re: Daytime Iridium Flares - plus more Resent-Date: Mon, 9 Feb 1998 04:54:51 EST Resent-From: SeeSat-L@cds.plasma.mpe-garching.mpg.de 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 UTC 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. Maybe 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 much? 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.