re: Iridium flare seasons

Walter Nissen (
Wed, 12 Aug 1998 10:53:56 -0400 (EDT) ("Matson, Robert") writes: 
>         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 
I think quite a long time ago, Jim Cook asked why the local incidence of 
Iridial glints is so scattered or so variable.  Perhaps he contrasted them 
to ordinary passes.  There were many lengthy replies, through which I'm 
sorry to say I never found the energy to plow.  But it seemed to me then, 
and now, that the simple answer is that ordinary passes are visible over 
very wide areas, with a good bit of fairly close repetition for most 
objects (generally speaking, those with inclinations significantly 
different than the observer's latitude).  By contrast, Iridial glints can 
be viewed only from within narrow (more or less North-South) tracks, which 
don't repeat at close intervals, especially if one looks only for the very 
brightest glints.  I expressed this by e-mail to Jim, but didn't mention 
it here. 
It is not clear to me how this may be related to seasonal variation. 
Less bright glints will occur in the same part of the sky, actually same 
part of an orbital plane, often numerous times per evening, often every 
night for weeks.  The central area of the glint tracks for any one evening 
will tend to bounce around (I'm not sure why this occurs) from place to 
place to the West and East.  When one happens to land on you, you see an 
extremely bright glint.  Or at least, you do, if the attitude of the 
satellite is close to nominal.  When Iridium lets the attitude of an 
object drift, the predictions are not so accurate.  We could try to 
organize observations find out if this attitude pointing is somewhat 
Focusing on repetition, the Tselina-2's and their Zenit-2 rocket bodies 
are pretty incredible.  I recall one which passed between Alkaid and 
Mizar, the stars at the end of the handle of the Big Dipper, on 8 
consecutive nights.  These objects are the Cosmos objects which have 
rocket bodies of 10.4 m length in the Molczan file, C* 2360 back thru C* 
Walter Nissen          
-81.8637, 41.3735, 256m elevation