These satellites carry television cameras that take pictures of the Earth's surface showing how the clouds move through the atmosphere. They also show snow and ice. By studying the pictures, weathermen can discover and inform people of approaching weather conditions. Communication satellites make it possible to send radio messages, telephone calls, and television programs between distant parts of Earth. These satellites are classified passive or active depending on the way they operate.
Passive communication satellites act as a mirror for radio waves.
A sending station on Earth beams waves to the satellite, the waves bounce off the satellite, and return to Earth. They reach a receiving station perhaps thousands of miles from the sending station. Active satellites receive signals from sending stations, amplify them, and send them back to Earth. Navigation satellites help pilots and sailors find their exact positions in all kinds of weather. Navigators can use it to find their position much as they would use a star.