Any object in orbit around a celestial body is called a satellite. Earth has had its own natural satellite — the Moon — for billions of years. Since 1957, however, hundreds of artificial satellites have been launched into orbit around Earth, each transmitting a cacophony of radio signals to locations across the planet. Satellites are now vital to modern life and are used in many areas of technology, including communications, entertainment and espionage.
But usually when someone says “satellite,” they are talking about a “man-made” satellite. Man-made satellites are machines made by people. These machines are launched into space and orbit Earth or another body in space. There are thousands of man-made satellites. Some take pictures of our planet. Some take pictures of other planets, the sun and other objects. These pictures help scientists learn about Earth, the solar system and the universe. Other satellites send TV signals and phone calls around the world.
Satellites fly high in the sky, so they can see large areas of Earth at one time. Satellites also have a clear view of space. That’s because they fly above Earth’s clouds and air. Before satellites, TV signals didn’t go very far. TV signals only travel in straight lines. So they would go off into space instead of following Earth’s curve. Sometimes they would be blocked by mountains or tall buildings.
Phone calls to faraway places were also a problem. It costs a lot and it is hard to set up telephone wires over long distances or underwater. With satellites, TV signals and phone calls can be sent up to a satellite. The satellite can then send them back down to different spots on Earth.
There are dozens upon dozens of natural satellites in the solar system, with almost every planet having at least one moon. Saturn, for example, has at least 53 natural satellites, and between 2004 and 2017, it also had an artificial one — the Cassini spacecraft, which explored the ringed planet and its moons.
Artificial satellites, however, did not become a reality until the mid-20th century. The first artificial was Sputnik, a Russian beach-ball-size space probe that lifted off on Oct. 4, 1957. That act shocked much of the western world, as it was believed the Soviets did not have the capability to send satellites into space.