The moon is natural satellite of the earth that circles along a fixed orbit. Artificial satellites, onthe other hand, are majufactured ‘moons’ that move around the earth. Most satellites carry some type of radio transmitter and receiver. Artificial satellites can be classified according to the tasks they perform.

Weather satellities carry television cameras that take pictures of the earth’s surface. By studying these pictures, weather forecasters can make weather predictions. Navigation satellites help pilots and sailors find their exact positions in all kinds of weather.

Communications satellites make it possible to send radio messages, telephone calls, and television programmes between distant parts of the earth. They receive signals from transmitting stations, amplify or strengthen them, and send them back to the earth. It is thanks to them that you can watch such channels as BBC, Star Plus and Zee TV.

Military satellites are used for communications, navigation, weather forecasting and mapping. ‘Spy’ satellites, designed for strictly military purposes, can photograph enemy ground forces and warships at sea. ‘Warning satellites’ can guard against surprise missile attacks. The United States and Russia have even worked on the development of ‘antisatellite’ systems that can interfere with another nation’s satellites.

NOTE: The first artificial satellite, Sputnik 1, was launched by the USSR in 1957.