Now that Tiangong-1, China’s first space station, has burned up in the atmosphere and crashed into the Pacific Ocean, you might be wondering what else is up there orbiting overhead.

When you step outdoors at night and see a moving light up in the sky, do you wonder what it is? We often assume it’s an airplane. If it’s blinking or red, that’s most probably what it is. Nowadays, however, it’s not uncommon to see a steady, colorless point of light moving high above you. This may well be one of the several thousand artificial satellites that a handful of nations have launched into Earth orbit since the beginning of the Space Age just over 60 years ago.

Varying in altitude from 100 miles to many thousands of miles, you can see some of these objects moving across the sky on any clear night. Most are dim, and easily missed. However, some are impressively bright, such as the International Space Station (ISS) and the especially brilliant Iridium flares.

An object in low Earth orbit, such as the ISS at about 250 miles altitude, takes around 90 minutes to complete one circumnavigation, assuming its orbit is circular. Each of the more than two dozen Global Positioning System (GPS) satellites at 12,500 miles altitude takes 12 hours to circle the Earth. At 22,236 miles above the equator the period becomes 24 hours, thereby matching the rotation of the Earth. This orbit is known as geosynchronous or geostationary, because the object appears to remain at a fixed position in the sky. Here we find additional vital components of modern day technology, including weather satellites and communications payloads such as satellite TV.

But what makes satellite observing especially interesting is the fact that rocket scientists can very accurately predict when any of them will pass over your location. Several websites offer satellite pass predictions such as NASA’s,,, and my personal favorite,

Each year, about 150 tons of “space junk” falls out of orbit and reenters the atmosphere. Fortunately, it’s travelling over 17,000 mph, so the vast majority of this debris vaporizes and never hits the ground. So don’t worry about being hit by falling space debris; with no known human injuries, the odds are astronomical!

Instead, go to the above websites, find predictions for some of the brightest objects from your location, step outside, look up, and be an eyewitness to some of mankind’s greatest scientific and technological achievements. And don’t forget to wave at the astronauts and cosmonauts on board the International Space Station when it sails overhead!

Resource: HVA club

The Heart of the Valley Astronomers is a group of amateur astronomers dedicated to sharing our passion for the sky with the local community. We meet on the second Tuesday of each month (next meeting: May 8 at 7 p.m.) at the Walnut Community Room, 4950 N.W. Fair Oaks Drive in Corvallis. Meetings are free and open to everyone. For more information, see, or visit us on Facebook.

Astronomy Question of the Month

Which satellite is the oldest man-made object still in orbit?

Answer to Last Month’s Question: How many stars can you see?

On a dark moonless night, well away from city lights, an average observer can see around 4,000 stars in an unobstructed sky. From the typical light-polluted suburban location, however, only about 900 can be seen at any one time.

Richard Watson is on the board of directors of Heart of the Valley Astronomers.


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