Even though NASA’s all-sky cameras are designed to detect meteors, nothing is perfect. Planes, lightning, clouds passing in front of the Moon, and bugs crawling on the plastic dome in twilight can trigger a detection, bringing either laughter or scowls when the video is reviewed the next day. Comparing vids from more than one station eliminates 95% of these “falses” – hard to imagine a bug that can be present at the same time on the MSFC and the Walker County cameras, which are separated by 90 miles! Even so, we occasionally pick up non-meteor events in both stations. These have to be caused by objects tens of miles up in the atmosphere, or even higher. Planes don’t operate this high, so that leaves one obvious explanation – satellites.
Anyone who has spent any length of time outdoors in the evening has seen a satellite, most likely the International Space Station. Very often, the satellite first appears as a faint dot of light over in the west, gradually increasing in brightness as it moves in a slow arc across the sky. Sometimes, it disappears in the haze near the eastern horizon; other times, the geometrical circumstances are such that the satellite will abruptly dim and disappear long before, passing into Earth’s shadow. Our all-sky cameras frequently detect the International Space Station, as it is the largest object orbiting Earth and reflects enough sunlight to outshine even the planet Venus.
However, there are instances when you look up and see a short, bright flash. These, too, are caused by satellites, or rather, sunlight reflecting off the solar arrays. Sometimes, a satellite’s attitude and orbit are oriented so that when it passes over your location, the solar array will reflect sunlight down to you, which will produce a star-like flash of light lasting a few seconds. If you pay close attention, you might be able to see that the “star” moves a little bit before it fades out.
The most famous of these “flashers” are the satellites that make up the Iridium constellation. They are communications satellites in low Earth orbit, used for satellite phones, and they have 3 very shiny, door-sized antennas that reflect quite a bit of sunlight. Iridium flares are very bright and very common; so common, in fact, that we can now predict when they will occur with great accuracy. You can go here to get predictions for your location.
Other satellites can produce flares as well, but because their shapes and properties are not well known, they cannot be predicted. But, you can use tools like the Heavens Above website to figure out which satellite caused that bright flash in the night, provided you make careful note of the time when it occurred. Last night, both NASA all-sky cameras caught a flare from Okean-O, a big Ukranian oceanographic research satellite launched back in July of 1999. Here’s an artist’s drawing:
So the next time you see a flash in the night sky, don’t run to the eye doctor or call the History Channel’s UFO Hunters. You probably saw a reflection from a satellite, and a little web research can even enable you to find the culprit and solve the mystery.
Takes about 5 minutes!