Rainer Kresken, email@example.com, writes: > Than the brightness changed periodically by several > magnitudes! The period was several seconds, I was just > to overwhelmed to make a decent measurement. I cannot > completely rule out that the brightness changes were caused > by clouds but it seems highly unlikely to me. I live in a light > polluted region and could clearly distinguish clouded and > clear regions in the sky. Low clouds are brightly illuminated. Higher clouds are much darker, and may be invisible even while the lower ones are quite obvious. We all know from daytime observations that higher cirrocumulus or altocumulus clouds are sometimes rippled, striped, or periodically puffy. These could easily cause the variations you report. I agree that when going out to observe Mir, cloud-caused periodical variation is an unlikely result. But this is quite different from saying that, given you saw a periodical variation, clouds are an unlikely cause. To judge that, we need to know what other possibilities exist and their likelihoods. We can rule out a silverized Russian flag flapping in the breeze. What else? Cheers. Walter Nissen firstname.lastname@example.org -81.8637, 41.3735, 256m elevation --- When or if the sky darkens at night, we can see Earth in her own environment as a precious ark of life plying the wine dark sea of cosmic space.