That's No Moon, It's a Space Station
You can see lots of interesting things in the night sky, even without a telescope. What are they? Everyday Einstein explains how to tell the difference between planets, stars, the International Space Station, and other celestial bodies.
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This modular design allowed the station to be launched piece-by-piece starting in 1998. The pieces were then assembled in space, with more pieces being added each year. While the final pieces aren't scheduled to be in place until the end of 2013, the station has been continuously occupied since November of 2000. Currently the ISS is about the size of an American football field.
The ISS orbits in what is considered a "low Earth orbit," which varies between an altitute of about 300 and 400 km each day. The ISS zips around the Earth at about 27,000 km/h, completing just over 15 complete orbits each day. That's over 11 times faster than an F-16's top speed.
See also: What Is "Supersonic"?
The ISS appears as a single bright light moving quickly across the sky from west to east. Planets generally appear to be much closer and have several blinking lights, while the ISS will appear as a single bright light moving relatively quickly.
If you’ve seen something that you think is the ISS, but you’re not sure, you can use websites such as ISS Tracker to verify the current location of the space station. This site can also be handy to help you plan when you should head outside to observe the station pass over your area of the world.
Satellites, Iridium Flares, and Other Space Junk
If you see what appears to be a dim star moving slowly across the sky, you’re probably seeing the sunlight reflecting off a man-made satellite, or piece of space debris. (Wherever mankind has traveled, you can always find litter). While there are currently tens of thousands of man-made objects floating around Earth (most of them inactive satellites or pieces of metal discarded from various space missions), only a few hundred are visible to the naked eye.
Among this pile of space junk are a famous group of satellites called the Iridium Satellite Constellation. The design of these satellites include 3 highly-reflective panels which frequently reflect bright bursts of sunlight down onto the earth, a phenomenon known as an “Iridium Flare.”
Even though this phenomenon is named for the Iridium satellite, it is the term used to describe when any satellite suddenly appears to “flare up” before fading back to its normal level of brightness.
So if you're staring up into the sky and you catch a glimpse of a dim moving light, about the size of a small star, that suddenly gets brighter for a few seconds, and then seems to fade away again, it is most likely an Iridium Flare, though not necessarily coming from an Iridium satellite.
So now you know some of the cool things you’re likely to see in the night sky. Of course there are lots of other things floating around in space: quasars, pulsars, globular clusters, comets, binary stars, and nebula, to name a few. Who knows, if you look carefully enough, you might just see a UFO—the universe is a big place.
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