In http://www2.satellite.eu.org/seesat/Jan-1998/0142.html Rob replied to my message comparing the brightness of an Iridium flare with the brightness of the not-too-far-away Moon. > Iridium brightness compared > > ROB MATSON (ROBERT.D.MATSON@cpmx.saic.com) > 12 Jan 1998 20:47:29 -0800 This is to express much appreciation for the explanation of the radiance versus irradiance of an Iridium flare versus the Moon. Rob, thank you very much! For the flare I wrote about, the Sun was at -6 degrees, so it was twilight as well as a poor location (UT Austin campus -- plus 75% Moon as I found out later -- although I guess moonlight isn't a big deal in twilight). So anyway my middle-aged, non-dark-adapted eyes probably saw it as, what, maybe about 20-50 times as intense as the Moon...? It sure made me wonder what the maximum theoretical magnitude of those things is. The brightest prediction I've seen from Iridflar is -8. It was high up (about 67 degrees), so extinction was not much of a factor. If I have one more question, it's what makes very bright flares -- from HST and a few others on rare occasions as well as the Iridiums -- appear to be extended light sources. My guess is that it's atmospheric refraction of the intense light and/or eye lens refraction and/or something about the way the light impacts the retina (which likely is not held still, for example).... Or is it just my eyes? Anyway, I suppose this also is involved to some extent in perceived brightness. That flare's appearance to me was as if it had been a significant fraction of the diameter of the Moon. Ed Cannon ecannon@mail.utexas.edu Austin, Texas, USA