Global Positioning Systems (GPS) have been around for sailors since 1990. It is the sailor’s modern way of determining everything we need, including longitude, latitude, time, speed, course, heading and distance, all at the touch of a button. The funny thing about this modern technology is that it is based on the same process of triangulation that we used on the boat. Remember how we needed three bearings to determine where we were on the chart? Well the GPS needs three “satellite fixes” to determine where we are as well. The way the computer plots our position is to figure out how long it takes for a certain radio signal to reach us from the satellite. Once again time is very important in determining our location. The radio signal is very weak, so it takes accurate computers to get an accurate reading. The signal is 1 ten quadrillionth of a watt. That is about equal to the light from a 20-watt bulb reaching us from 11,000 miles away. So although it is a great tool to have, we don’t want it to be our only source of navigational data. We still want to keep our own accurate measurement by using our compasses, watches, sextants etc.
Some mobile telephones and television services use satellites to transmit information.
The moon is a satellite to the earth. The earth is a satellite to the sun, so we live on a satellite!