RE: Iridium flare seasons

Allan Cook (
Mon, 10 Aug 1998 15:41:15 -0500 (CDT)

I wrote a basic program which plots the time of the flare on the y axis 
and the date on the x. In mid June, there are three groups including 
group 2 and 3 plus the group containing irids 65, 68, 73, 64 etc. The 
flares for my location (98.316W 49.941N) occurred about 0600, 0730 and 
0900. As the days progress, the flares occurred earlier for each group. 
By mid July they were at 0430 0600 and 0730. Of course, another group 
appeared around 0900. After the middle of August, the flares around 0630 
disappear, as they occur when the satellite is in shadow (probably). By 
the end of the month there is one group at 0300 and one at 1000.
   I have not included any passes that occur during the day. If I can 
figure out how to upload the program, I will. It runs on Dos Qbasic or 
the old GW-Basic. 

On Mon, 10 Aug 1998, Matson, Robert wrote:

> 	Hi,
> 	> Is there some way these changes can be graphically simulated?
> I
> 	> assume the planes drift (W to E)(??) producing this "seasonal
> 	> effect".  It would be interesting to "watch" this in some
> form.
> 	Actually, the sun is the culprit here rather than the satellite
> constellation.  The number
> 	of flares at any location appears to peak during solstices and
> drop around the time of
> 	the equinoxes.  I haven't explored the exact reason for this,
> but it must be a combination
> 	of the orbital inclination, the tilts of the MMAs, and the
> location of the sun about 90
> 	minutes after sunset or before sunrise.
> 	One of these days I'll try modifying a piece of code I wrote to
> plot Superbird A glint
> 	locations on a map, and change it to do Iridium glint tracks.
> The pattern of the
> 	tracks will probably be quite interesting, and go a long way
> toward explaining the
> 	seasonal variations.  --Rob