Iridium Flare

Satellite flare or satellite glint is the phenomenon caused by the reflective surfaces on satellites (such as antennas or solar panels) reflecting sunlight directly onto the Earth below and appearing as a brief, bright “flare”. With highly reflecting triple antennas, the Iridium communication satellites create the brightest flares in the night sky, some bright enough to illuminate night landscape for a short time. They create predictable and quickly moving illuminated spots of about 10 km diameter. To an observer this looks like an extremely bright flare in the sky with duration of a few seconds. However this flashing has been also a problem for serious deep sky astronomical study, as the flares occasionally disturb observations. When not flaring, the satellites are often visible crossing the night sky at a typical magnitude of 6, similar to a dim star. Here in this image Iridium satellite number 35 lit up the predawn sky west of Boston, as Sky & Telescope senior editor and TWAN team member, Dennis di Cicco, waited with his camera, taking a 10-minute exposure on Fujichrome 100 slide film through an 80-mm lens.