could Iridium flashes cause eye damage?

Joe Dellinger (jdellinger@amoco.com)
Sun, 14 Dec 1997 18:35:59 -0600

	At the local astronomy club meeting I gave a short presentation on
the Iridium flashes, to see if anyone else was interested in observing one.
One fellow with a whopper telescope (20-inch diameter) wanted to know what
would happen if he were unlucky enough to be looking at something at the spot
in the sky just where the satellite happened to flash. Certainly it would be
dazzling. Could it conceivably cause eye damage? If not in that size telescope,
what about in an even larger one?
	My first answer was "of course not", but then he told me that even in
his size scope it is dangerous to look at the moon without a filter. To back
this up he pointed out that he can make a piece of paper start smoking by
holding it at prime focus while his scope is pointed at the full moon.

	Hmmm. You can't make an extended source of light any brighter by
magnifying it. However, if the satellite makes a perfect mirror, then at SOME
(implausibly high?) level of magnification all you will see is the mirror-image
of the sun, and thus looking at the satellite should become, if for only an
instant, approximately equivalent to looking at the sun. That is certainly not
something you want to do.
	Has anybody tried "running the numbers" on this out of curiosity?
Granted, it would take extraordinarily bad luck to point at an Iridium flare
with a huge amateur telescope at high power by accident.