Iridium Flares!

For the last 10 years or so, it has become my daily habit to spend 15-20 minutes in my hot tub right before I go to bed at night. This time is spent relaxing/unwinding as well as thinking about the day past and the day to come.  It is also in my nature to spend some of that time observing the night sky.  I regularly see jets and satellites traveling high up in the sky and, since Central Vermont Medical Center is visible from my house, I frequently get the chance to see the medivac helicopter coming and going in the night.  When the time is right, at various times of the year, I have also get a ringside seat for some pretty spectacular meteor showers.

Last night, however, I had an amazing showing of something that I had both heard of and read about, but never seen… an Iridium Flare!  An iridium flare is caused by the reflection of the sun’s light off of one of the 88 Iridium Satellite LLC’s communication satellites, which are orbiting approximately 485 miles above the earth’s surface.  These satellites are a part of a global communication network that allows mobile and pager usage anywhere on earth; including both poles.  The satellites are arrayed such that at least one of them is constantly providing overlapping coverage for every inch of the earth’s surface and there are several of them that pass over the central Vermont region.

iridiumEach of these satellites has 3 highly-polished, silver-coated teflon antennae which provide mirror-like reflectors for sunlight.  When one of these satellites passes over your location, there is a small chance that it will be oriented in such a way as to send that reflected sunlight to you.  While these satellites are passing over your location 24 hours a day, the reflections that they produce are, under normal circumstances, only visible at night.  The reflected sunlight from these satellites is very bright; the brightest measuring in the range of -4.0 to -8.5, using the same scale of magnitude used to measure the apparent brightness of stars.  For your reference, the brightest star visible in my night sky is Sirius (part of the Canis Major constellation… look slightly “southeast” of the easily recognizable Orion’s Belt) at only a magnitude of -1.46, the brightest planet is Venus with an apparent magnitude of -4.6 and the full moon on a clear night shines with a magnitude of about -12.  You can easily tell that these flares, when visible, can definitely be one of the brightest visible objects in the night sky!

These flares, however and unfortunately, last only a short amount of time… approximately 30 seconds… and are visible in only a very narrow region… only about 10km wide on the earth’s surface… so your chances of simply looking into the night sky and seeing one of these flares is pretty slim (though it worked out well for me!).  Fortunately there are Websites and smartphone apps that make it pretty easy to determine an optimal time for taking in one of these flares.  For Websites I would recommend  Once you enter your location information… this can be done by either browsing using a map or, if you already know it, manually inputting the Latitude/Longitude of your current location.  The “Iridium Flares” page will then show you the visible Iridium flare for the next week (at night) at your location.  For smartphone apps (I looked at many and I use Android), my favorite of the moment is called ISS Detector, which is available for free from the Google Play store.  In addition to providing information about the ISS (International Space Station), which is also visible in the night sky, you can get viewing information for Iridium flares as well many other bright man-made objects in the sky. One of the best features offered by this app is the fact that it takes the weather for your location into account when highlighting upcoming viewing opportunities… a cloudy sky means no visibility, of course… thus maximizing the chance of you seeing one of these relatively rare events.

My first Iridium Flare viewing happened by chance, but that is certainly not the way that my next viewing will take place.  From my hot tub I have an unobstructed view of only about 30% of the night’s sky, but using the Websites or smartphone apps, it should be easily possible to determine when my next opportunity will take place… and I am looking forward to it!

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