Source of brilliant HST flashes

Ed Cannon (
Sat, 01 Mar 1997 02:46:44 -0600

Before clouds moved in Friday night, I was fortunate enough to see a 
great HST pass which included another of those fantastic specular flashes
to magnitude -5 or so.  HST bisected Orion, and before the flash it was as 
bright as Rigel and Betelgeuse.  Then the flash, which had an appreciable
duration (half a second or more?), was *MUCH* brighter than nearby Sirius.  
Also, brightness increased noticeably just before the flash, and then 
decreased in a more-or-less symmetrical manner back to non-flash magnitude.

A while back (7 Feb., message 0801.html on the Oxford mirror site) Robert 
Reeves ( suggested that HST's solar panels appear to 
be too bowed to produce such flashes.  After seeing some photography of HST, 
he suggested that they must be coming from the aperture door.  Now, after 
seeing some pictures of the STS82 mission, I am wondering if the flat bottom 
of HST could also produce the flashes.  With HST aimed away from Earth, its 
approximately 2-meter diameter bottom faces the ground.  In the photos of 
the recent mission, it appeared to me that the bottom is as shiny as the 
rest of HST.  And I believe the bottom is larger than the aperture door, as 
well as free of any possible obstruction.

Anyway, if either of those flat surfaces produces the flash, then given 
precise enough details of a flash observation, someone who knows how could 
probably figure out the RA and Dec towards which HST was pointed!  I'm sorry 
to say I didn't get precise data on the time of this specular flash, except 
that it was probably a few seconds before culmination, which was 1 March at 
1:30:04 UT; location: latitude 30.308 north, longitude 97.728 west.

By the way, as I'm not very good at such math, I'll ask how large would the 
flash track on the Earth be, say if it was produced by a flat, two-meter 
mirror?  HST's range at culmination was about 667 km.

Also saw Lacrosse 2 (91-17A, 21147) and 3 other objects.  Looked several
times in Superbird A's direction with a small 8x21 monocular, but besides
a limited instrument and poor location, the obs. were sporadic, so I didn't 
see any flashes (assuming that it still is flashing on Central Texas).

Ed Cannon
Austin, Texas, USA
30.308N, 97.728W