Global Positioning System
Most people have been lost at one time or another, but what if it were possible to know where you are, anywhere on Earth, 24 hours a day? The Global Positioning System (GPS) can give that information, and it is free to anyone with the proper equipment and a basic knowledge of mathematics.
In the 1980s, the U. S. Department of Defense designed GPS to provide the military with accurate, round-the-clock positional information. Twenty-seven satellites orbiting over 10,000 miles above Earth regularly send information back to Earth. A small piece of equipment, called a GPS receiver, uses this information to compute its position to within a few yards. GPS receivers used for surveying can find positions to within less than one centimeter.
The "constellation" of satellites above the Earth is constantly changing; each orbits Earth twice a day. At any given time there are enough satellite
signals to accurately locate oneself in three dimensions: latitude, longitude, and elevation.
GPS is rapidly becoming a common technology, but it is still a mathematical wonder. Ancient sailors looked to the heavens to estimate their position in the vast oceans. Modern sailors also look to the sky for information, but the modern positioning information they receive is so accurate that any errors are less than the width of the pencil they use to mark their map.
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