Skywatching for Artificial Satellites

By Stephen P. Maran

Hundreds of operating satellites are orbiting Earth, along with thousands of pieces of orbiting space junk — nonfunctional satellites, upper stages from satellite launch rockets, pieces of broken and even exploded satellites, and tiny paint flakes from satellites and rockets.

You may be able to glimpse the reflected light from any of the larger satellites and space junk, and powerful defense radar can track even very small pieces.

The best way to begin observing artificial satellites is to look for the big ones — such as NASA’s International Space Station or the Hubble Space Telescope — and the bright, flashing ones (the dozens of Iridium communication satellites).

Looking for a big or bright artificial satellite can be reassuring to the beginning astronomer. Predictions of comets and meteor showers are sometimes mistaken, the comets usually seem fainter than you expect, and usually you see fewer meteors than advertised. But artificial satellite viewing forecasts are usually right on. You can amaze your friends by taking them outside on a clear early evening, glancing at your watch, and saying “Ho hum, the International Space Station should be coming over about there (point in the right direction as you say this) in just a minute or two.” And it will!

Want to know what to watch for? Here are some characteristics you can pinpoint for both large and bright satellites:

  • A big satellite such as the Hubble Space Telescope or the International Space Station generally appears in the evening as a point of light, moving steadily and noticeably from west to east in the western half of the sky. It moves much too slowly for you to mistake it for a meteor, and it moves much too fast for a comet. You can see it easily with the naked eye, so it can’t be an asteroid — and, anyway, it moves much faster than an asteroid.

    Sometimes you may confuse a high-altitude jet plane with a satellite. But take a look through your binoculars. If the object in view is an airplane, you should be able to distinguish running lights or even the silhouette of the plane against the dim illumination of the night sky. And when your location is quiet, you may be able to hear the plane. You can’t hear a satellite.

  • An Iridium satellite is a wholly different viewing situation: It usually appears as a moving streak of light that gets remarkably bright and then fades after several seconds. It moves much more slowly than a meteor. And an Iridium flare or flash is often brighter than Venus, second in brilliance only to the Moon in the night sky. The Sun, located below your horizon, reflects off one of the door-size, flat, aluminum antennas on the satellite to cause the flash of light. At star parties, people cheer when they spot an Iridium flare, just like when folks see a fireball. You can even see some Iridium flares in daylight.

    And consider this: More than 60 Iridium satellites are in orbit. They interfere with astronomy, and professional astronomers want them to disappear, but until now at least the satellites have had a “flare” for entertaining us. A new generation of the satellites, called Iridium NEXT, are being launched (the first ten went up into space in January 2017). The NEXT satellites may be next to useless for amateur flare watchers because the design of the antennas has changed so that bright reflections from them are unlikely. The good news is that retiring all the original Iridiums will take a while, so if you start looking soon you may be able to catch some impressive flares before they’re just history.