Iridium Satellites are a constellation of communication satellites that allow some phones to make calls even in areas where there is no normal cellular coverage. They also have a peculiarity: they have three solar panels and one communication antenna that are highly reflective, and work as very good mirrors. Usually, near the sunset or sunrise, if they are illuminated by the sun, they might reflect that light to the Earth surface, in a fast moving circle with a diameter of around 20 km.
If you are on the ground, and one of the solar panels illuminates your position, you will see a star that suddenly appears in the sky, moves a little bit, and disappears. I cannot imagine how many people in the recent years might have incorrectly confused this with an UFO. The few seconds the event lasts are interesting the first times that happen, but afterwards you get used to it and it loses all its interest.
It’s something different if the main antenna is the one illuminating the Earth, especially if the satellite is passing near the top of your heads (at least over 45 degrees altitude in the sky). In this case is not a “normal” star what appears, but one similar in brightness to Venus. The flare, which lasts a few more seconds (15-20 approx.) is very hard to miss, and very spectacular. You are looking at the sky and suddenly a dim star appears. At the beginning it looks like a normal star, but then you notice that it is moving, relatively fast, in a straight line. It keeps winning a little bit of intensity until, in a couple of seconds, it starts to flash brightly, until finally reverses all the process and disappears dimly after a few more seconds.
Today’s picture captured Iridium 34 satellite in one of those flights. With an exposition of 20 seconds and a “rearming” period of less than 1 second, I was pretty sure I would capture it. But Murphy’s Laws are unavoidable, and it turned out that the exposition time expired just in the maximum point, and the rearming period avoided me to capture all the process. At least I was half-lucky, and the picture ended just in the maximum, so I got a decent picture that looks like a meteor. This picture corresponds to the period between the satellite starts to glow dimly until the maximum. Afterwards, a symmetrical trail in the right part would have resulted if the exposition had continued.
Even if you are not a photographer, finding an Iridium flare is a nice activity for summer nights. You will learn how to locate an object in the firmament, and how to recognize some constellations in the process. For a flare of the main antenna (which has a magnitude of around -7) you don’t even need to be in a dark place, and can be seen even in the middle of a city, as long as the buildings don’t obstruct the vision of the sky.
Do you want to locate one? Try Heavens Above. This page allows locating the ISS and Iridium satellites (among other dimmer satellites) for any place and time. Do you have kids? Tell them that you will make a star appear when the moment happens, and gain their awe, crowning you as the “Master Prophet Of The Stars”.