By David Ward
Have you ever seen a bright flash in the night sky, brighter than any star and lasting just two or three seconds? If so, you may have witnessed a phenomenon known as an Iridium flare.
There are an estimated 3,000 spacecraft orbiting the earth right now. Sixty-six of these belong to a special class of satellites known as the Iridium Communication Constellation. Their job is to provide a worldwide network of communication and data exchange. Each of them has three door-sized antennas which can periodically reflect sunlight below to the surface of the earth.
Amazingly, these flares are predictable because the satellites are controlled and computer programs can assess the orientation of the antennas. Go to the website heavens-above .com or simply google Iridium flare sighting. You will have to enter your exact latitude and longitude because each flare only covers an area about 6 miles across. You will get the time, the direction in the sky and the brightness of the event. There will often be several flares visible each night from your location.
There is lots of stuff up there in the sky, so how do you know if you are seeing one of those flares? First of all it will be bright, very bright, brighter than any star, brighter than Venus even. It will only last a few seconds and it will be seen in the twilight or just after it gets dark. In the middle of the night, the earth’s shadow will be right overhead. Any satellite up there will not have the sun shining on it, so no flare is possible.
If what you are looking at is moving across the sky and has a blinking red light on it, then it is an airplane. If it streaks across the sky leaving a trail for a few seconds, then it is a shooting star. If it is as bright as the brightest stars and moves steadily across the entire sky, it is the International Space Station. If it moves erratically, flashes on and off and makes weird, spooky noises, then it is a flying saucer.
500 miles up
You probably will not be able to see the satellite itself, though you may catch a glimpse of it in binoculars. Iridium satellites orbit the earth at about 500 miles up, quite a bit higher than the International Space Station.
These satellites are not made out of iridium, which is used as a hardening agent in platinum alloys. The name comes from the Greek goddess Iris, goddess of the rainbow, and a messenger of the gods. The ancient Greeks are behind everything up there in the sky. A messenger goddess fits in nicely with a network of communication satellites or maybe somebody just thought the name sounded cool.
Some astronomers consider these satellites to be just another form of light pollution which can easily spoil a carefully planned hours-long photo of the night sky. I always enjoy pointing one out along with the International Space Station at a star-gazing event. A sighting never fails to bring out an audible response from everyone. In 2009 Iridium No. 33 collided with a defunct Russian satellite over Siberia, creating thousands of pieces of space junk which will orbit around us for years to come.
Do you want to see something farther away than satellites? There is plenty to look at up there now that the bright stars of winter are coming into view. Orion, the hunter, is sliding up into the southeast with two very bright stars at his upper left and lower right corners. Below and to the left of Orion, super-bright Sirius, the brightest star in the sky, twinkles madly and is often mistaken for a UFO. Up above the hunter, my favorite little star cluster, the Pleiades, sparkles like diamonds sprinkled on black velvet.
There are not a lot of clear nights this time of year, so if we have one, be sure to go out and soak up some of the wonders above.