Iridium Flare
July 25, 2002
Provided by: Geoff Sims
Summary authors & editors: Jim Foster
The above photo shows sunlight reflecting off of one of the Iridium series of telecommunication satellites. Known as an Iridium Flare, this one was a magnitude -8 and was observed at 6:58 p.m. local time near Sydney, Australia in August of 2001. FUJI Superia 400 film was used with an exposure of 40 seconds, at f/3.5 - the photo was taken by Geoff Sims with a Nikon F70 camera.
The Iridium satellites have near-polar orbits at approximately 485 miles (780 km) above the Earth's surface. The source of the flaring is sunlight bouncing off the satellite and then reflecting back towards Earth. If the geometry is just right with the Iridium satellites, the Sun and observers on the Earth, these satellites will flare up for five seconds to as many as twenty seconds, and then they'll quickly seem to turn off. Satellite glint is a common occurrence with most all satellites, but the construction of these Iridium birds accentuates the light that's reflected.
The flare shown above is exceptionally bright (more than 200 times brighter than the brightest stars we can see). Most flares are best seen after dusk or before dawn when the Earth is darkened, but the satellite is still illuminated by the Sun, however, many flares can be seen in daylight if you know when and where to look - see the Heaven's Above link below. Some observers have mentioned that when the satellite "flares," it looks like a headlight beam shining in the darkness. The reddish streak at the right center of the photo is a jet contrail.
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