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COPYRIGHT 2002 International Technology Education Association
Have you ever spotted a satellite crossing the night sky over your town or city? Although it may have been a mere point of light like a star or planet, you could not mistake a visible satellite for a star, a planet, or even a high altitude plane. The reason? Even a plane does not move across the sky as fast as a satellite.
The International Space Station (ISS) is the easiest satellite to spot because it is by far the biggest, and its orbit is low compared to many satellites. Take a look on NASA'S list of ISS viewing opportunities at www.hq.nasa.gov/osf/ station/viewing/issvis.html to see whether the Space Station might be visible from your location. If so, make plans to look for it.
Just how fast does the Space Station travel? And how does it (or any other satellite) stay in orbit? Why doesn't Earth's gravity just bring them crashing down? Why and how do they travel so fast? And how do spacecraft engineers here on Earth control them?
Weightless? No Way!
Satellites take advantage of some basic laws of physics that two scientists figured out around 400 years ago. Johannes Kepler, a German astronomer and mathematician, discovered that the time it takes for one body to orbit another (like a planet to orbit the Sun) is directly related to the distance between the bodies. For example, he discovered that it takes Jupiter (the 5th planet from the Sun) 12 years for one orbit, while Saturn (the 6th planet) takes about 29 years for one orbit. Isaac Newton, English scientist and mathematician, came along a few years later and discovered the direct relationship between mass and a force he called gravity, which acts to keep the planets in orbit about the Sun rather than shooting off into...
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