Wednesday, January 12, 2011

Heavens Above

Northern Lights and Iridium Satellite flare light up the Alaskan sky-photo by Jason A

A few years ago, as part of St. Louis Community Colleges “Master Naturalist” certificate program, I signed up for a short course on night sky viewing, sponsored by St. Louis Astronomical Society. Our instructor, Mike Malolepsky, took us out to the center of campus in the twilight to see an Iridium flare. He explained that the Iridium communication satellites—there are 66—have flat-surfaced antennas, shielded with shiny aluminum. As the satellite rotates, sunlight glints off these mirror-like panels. When the angle between the panel and the sun is just right, that flash hits a small area of the planet, visible to anyone looking in the right spot.
Mike pointed to the right spot and we stood around, looking up. A small crowd of curious students began to gather around us. Then POW—a small but brilliant flash of light appeared in a sky that was still bright. Two young women in the crowd, who had not heard the explanation, actually clutched each other in fear. Possibly they envisioned an impending alien abduction. The flare lasted for several seconds, and those of us who were informed were just as stunned as those who weren’t.
The magnificent photo above, taken by Jason A. about 30 miles east of Fairbanks, Alaska, shows an Iridium satellite flare in a sky colored green with the aurora borealis. The view in the photo is not quite the same as what we see. Jason left the shutter open for 15 seconds in order to capture the light. The observer sees a burst of light, but the photo shows a streak as the flare moves from left to right, as Jason explains. Just as wonderful is the reflection of the flare and the green sky in the lake. Thanks for making this photo available to us, Jason!
How in the world did he get such an image? Was it just luck that his camera was pointed at this precise area of the sky? And how did Mike know where and when to tell us to look? The answer to this riddle is our Wednesday website: Heavens Above. Chris Peat maintains this site that gives predictions for the movements of satellites, International Space Station, planets, sun, moon, and even minor planets.
Heavens Above
For accurate information, you’ll want to register and log in. Seeing a flare depends on your latitude, longitude, and elevation, all of which you record for your location when you register. The prediction is given in local time, using the 24-hear clock, and intensity or magnitude. For those new to astronomy like myself, lower numbers mean a brighter flare. Thus, a flare of a –8 magnitude is predicted to be brighter than a –4. The table also provides the altitude, or angle from the horizon to the point of the flare, and the azimuth, or direction in which to look, measured in degrees of the compass; north is 0°, east is 90°, and so on. Peat even tells you which satellite you’re viewing! Global Positioning Systems (GPS) are helpful I’m sure, but not necessary. Bring your binoculars along when you step out to view an Iridium flare—amazing!
Can’t get enough Iridium flares? Explore the photos in the Flickr group, “Iridium Flares!” Many of the members in this group share advice to photographers about exposure, etc. For more links and diagrams, check out the Visual Satellite Observer’s pages.

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