Astro photography

iridium flare

The Moon, Jupiter, and an Iridium Flare, May 10, 2010. As the Moon and Jupiter rose above Georgian Bay, and Iridium flare briefly brightened the sky above them. This photograph was taken at 4:28 a.m. EDT.

Iridium flares are caused by particular communication satellites that have large, mirror-like antennas that sometimes reflect sunlight directly onto the Earth below. If the angles are just right, the reflected sunlight can be very bright — in this case, it was magnitude -5. The positions of Iridium satellites are precisely known, so it's possible to predict when and where a flare will be seen.

Here's an example of an Iridium flare above Keppel Henge.

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Steve Irvine
R.R. # 2
Wiarton, Ontario
Canada N0H 2T0
(519) 534 2175