The observation and imaging of Iridium flares has become something of a cult. Iridium satellites' sole purpose is to assist in global communications (digitized phone calls, wireless electronic mail etc) and number 66 in total now that current orbiting plans are complete where eleven satellites have been allocated to six equally-spaced orbital planes covering the entire surface of our planet (original plans called for eleven satellites across seven orbital planes and, hence, for the name Iridium which represents the 77th element of the periodic table). These satellites are placed in low-earth orbit and completely circle our planet every 100 minutes (or 14.34 times/day).

Iridium flares represent the unique occurrence in space and time where the panels of the satellite perfectly redirect the solar or lunar light onto an observer on the planet's surface. Aside from the silhouette images that one can capture during a solar transit (see my web page dedicated to solar and lunar transits), Iridium flares represent the only other means by which a ground-based observer can detect or observe a satellite during the day. With a peak magnitude of about -8.4, these flares can easily compete with a well-developed crescent moon during darkness and can be quite visible during the day as well.

Although you may see references to Iridium satellites with an ID greater than 66, for approximately 88 such satellites have been launched to date, the ultimate number still remains at 66 Iridiums. The excess represent back-ups, various failed missions and some still not in their proposed operational latitude.