Re: Different flash period for 95 58B?????

Tue, 16 Jan 1996 04:57:41 +0100 (CET)

Ron Lee writes :

>I just finished observing 95 58 B  (23705) on 16 Jan 96 UT on a 53 degree
>pass from the NNW to SE from Falcon, CO.  The approximate period while at 0
>deg azimuth, 25 degree elevation was 0.49 sec (49.11 sec for 100 flashes)
> starting about 109 UT.  Just after passing Capella, azimuth 70 degrees, 52
>degrees elevation, the period was about 1.01 sec (50.26 sec for 50 flashes).
> Given that I may have miscounted the number of flashes, the period was
>double when abeam me compared to when due north.  Why the apparent

Presumably, you were counting secondary flashes during your first 
measurement at 25 degree elevation. A cylindrical body like a rocket will
usually give off 2 bright flashes per rotation period, due to reflection of
the sunlight on the body of the cylinder (one every 180 degrees). If the
rocket has reflective structures at the (usually more flat) *ends* of the 
cylinder, secondary flashes may appear, under favourable conditions. As the
illumination geometry changes during the pass, those secondary flashes can
disappear, which is probably happened during the pass you observed.

I would guess that you miscounted during the second measurement, there were
probably 51 flashes instead of 50, with a flash period of 0.985 sec. This
is, within the bounds of the synodic effect, the double of
your first measurement. Miscounting on your first measurement would mean 
counting 2 flashes too much. Not impossible, but less probable, I guess.

The maximum possible synodic effect is 0.002 sec for a 1 sec flash period, so
it's unlikely that the synodic effect is to blame for the discrepancy.

Thanks for reporting your observation, Ron, this gives me the opportunity to
plug the activities of the Belgian Working Group Satellites, which is 
collecting and archiving flash period observations, for research purposes. 
The archive is available to anyone interested (e.g. at the seesat-archive or 
the oxford ftp-site), and regular articles with analysis of the archive appear
in the bimonthly newsletter Flash. I am also preparing an article in a 
refereed journal. There is some interesting science in there!

So, if you're getting tired of just looking at satellites and want do some
fun observations that are useful, send your observations to Tristan Cools
<> who is our official 'observations collector'. You can
ask him or me (or any of the other active people from the BWGS that are also 
on seesat-l like Kurt Jonckheere, Leo Barhorst, Bram Dorreman,...) about
flash period observing. Or, check out our Web-pages at :
   Bart De Pontieu