In the early 1800's Midshipmen's education on board a vessel like the Constitution included navigation; how to determine the ship's location at sea. How do you determine your location if there is no land in sight? Each day at noon, Midshipmen measured the sun's position above the horizon using a sextant. Then the ship's position was calculated using the measurement taken with the sextant and mathematical equations. The sextant was a tool that was used consistently for navigation.
Today, it is still being used to navigate the most difficult conditions. Thanks to modern technology, the current tool used for finding ships location is a GPS. The Global Positioning System (GPS) is a constellation of navigation satellites that orbit the Earth at an altitude of about 12,000 miles (20,000 kilometers). At this altitude, the satellites complete two orbits in a little less than a day. Though originally designed by the U.S. Department of Defense for military applications, the federal government made the system available for civilian uses and lifted security measures designed to restrict accuracy to 10 meters. This made the GPS the ideal tool for the marine shipping industry, and boat captons of pleasure boats as well. The optimal constellation consists of 21satellites with 3 operational 'spares.'
The system is designed to ensure that at least four satellites are visible at least 15deg above the horizon at any given time, anywhere in the world. Engineers and scientists are always coming up with new applications for established technologies such as GPS! For example, during the recent H1N1 FluOutbreak, the GPS system was used to create immediate mapping of cases of the flu as they were reported.
Try this activity to make and use your own sextant
Try this one to learn more about GPS
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