Iridia

Leo Barhorst (leobarhorst@pi.net)
Mon, 08 Sep 1997 22:45:53 +0200

Hello Iridium observers,

Last night I've observed the complete 97- 30 family of Iridia.
See also my 970907 observation posted separdly to seesat-l.

Between 19:41 UT and 21:04 UT six of the seven Iridia from the 97- 30 launch made a pass 
visible from Alkmaar. The first was low in the northeast, the last almost overhead from 
north to south.
As the maximum elevation became higher and higher the maxium brightness of the Iridia 
also grew untill about 45 degrees and mag -3.
The last two obs probably belong to the next group of passes of which I didn't see 97- 
30 B, G, E, A and F on their 47 to 30 degress elevation passes in the west.

With Track16b I've made a 1 minute output of the observed passes.
The results are summerized below: given are the figures of the highest Alt in the pass 
and the time of the obs.

Sat     UT    Sun    Azi   Alt     Ut obs
97-30B 19:42:18 -13.2  71.75 30.13 19:41      almost S, mag 6
97-30E 19:51:18 -14.4  69.38 34.78 19:51      slowly var, mag 6->7
97-30A 20:00:18 -15.6  63.29 39.76 20:00:48.9 flare to mag 3; otherwise mag 6
97-30F 20:10:18 -16.9  89.62 47.39 20:09:53.5 flare to mag -3; total flare 7 seconds
97-30C 20:56:18 -22.2 264.37 76.59 20:57      var, mag 4->5
97-30D 21:05:18 -23.1 254.36 64.80 21:04      almost S, mag 6

97-30G made a pass before 19:40 UT below 25 degrees elevation.

>From the above its clear that the flares do occur when the sat is at about 45-50 degrees 
elevation.
More study is needed to fully understand this phenomina and what causes it.

At 20:47 and 20:48 UT I saw the two 'dummy' Iridia from the 97-48 launch. First came 
object A; 1 minute later followed by object B. At the same time 95-32 B made its pass at 
almost the same track although much higher at about 1000 km. As I watch I saw 95-32 B 
grow slowly brighter and then 97-48 A overtook it; then 95 -32 b faded away before 97-48 
B came along. Quite a nice view.

BTW the photo Paul took and put on Seesat is very good. I use it to show other people 
what it is about, this Iridimania.

This brings me to another point.
As the number of Iridia and other LEO-sats (no not my sats but Low Earth Orbit) will 
grow considerable over the next years it could be a good idea to make a separate Iridia 
PPAS to avoid the real PPAS to become to much filled with steady and flare observations.
I don't report MIR obs to PPAS; although p.e. the MIR-Progress sequence was reported to 
Seesat.
This FLARE can consist of two parts:
1. FLARE.OBS in the standard PPAS form so the obs are compatitable with the other PPAS 
observations;
2. FLARE.DAT in the by Paul, Ron and Walter proposed Iridium format.
Any comments to my own e-mail adres. I'll collect them and put a summarization on 
SeeSat-L.

Greetings and clear skies, 
-----------------------------------------------
Leo Barhorst    Alkmaar   The Netherlands
52.65 North   4.77 East   3 m asl
-----------------------------------------------
Every day I wonder about what I see in the sky