Iridium flares are nothing more than the sun’s reflection off the communications satellites owned by the Iridium Satellite company and used for satellite phone service. The antennas of these satellites are positioned in such a way that they can brilliantly reflect the sunlight, producing a brief spectacle in the night sky, known as a glint. Sometimes, the flare is so bright, it can even be seen during the day.
The antennas that produce the iridium flares seen from the ground are not what many may imagine when they hear the word. Rather than being made from iridium, a metal similar to platinum and used for its harness, the antennas on these satellites are plates of highly reflective aluminum. Each satellite has three antennas with a height of 6.2 feet (188 cm) and a width of 2.5 feet (86 cm).
Iridium flares are different from the normal occurrence of seeing a satellite cross the night sky. In darker areas, seeing satellites is a commonplace event. Stargazers can readily point these out to newcomers as they see them move steadily from one side of the horizon to the other, sometimes fading in and out of view.
Instead of these typical occurrences, Iridium flares are a brilliant flash of light as the satellite’s antenna catches the sun at just the right moment. They usually only last a few seconds, so unless stargazers are actually looking for them, they can be quite easy to miss. However, with some 66 active Iridium satellites in orbit, there are plenty of opportunities.
It is hard to say for certain when the first glint was spotted, but photographs of the flares date back to 1997. At the time, the flares were considered unpredictable. Those wishing to see them now, however, have an advantage. Astronomers can predict when and where they will take place and websites detailing this information have been created. In addition to predicting when Iridium flares will pass within your view of the horizon, these websites can also predict other passings of satellites, the space shuttle and the International Space Station.