Satellite

A satellite is an object that travels in orbit around a planet, moon, or star. The word covers two different kinds of things. Natural satellites are moons, like the one that lights up our night sky. Artificial satellites are machines that people build and launch into space. This entry is mostly about the machines.

The first artificial satellite was Sputnik 1. The Soviet Union launched it on October 4, 1957. Sputnik was about the size of a beach ball and beeped a simple radio signal back to Earth. Its launch shocked the United States and helped start the Space Race. Today there are more than 10,000 working satellites circling Earth, and thousands more old ones that no longer work.

Satellites stay in space because of how orbits work. A rocket carries the satellite high above the atmosphere and pushes it sideways at huge speed. Most satellites travel around 17,000 miles per hour. At that speed, they fall toward Earth, but Earth curves away beneath them just as fast. So they keep falling forever without hitting the ground. That is what an orbit really is.

Different satellites do different jobs. Weather satellites watch storms form over the ocean and help forecasters warn people about hurricanes. Communication satellites bounce TV shows, phone calls, and internet signals between faraway places. GPS satellites tell your phone or car exactly where you are. Science satellites, like the Hubble Space Telescope, study stars and galaxies far from Earth's blurry atmosphere. Spy satellites take detailed photos of the ground for military use.

Satellites orbit at different heights. Low-Earth orbit is only 100 to 1,200 miles up, where the International Space Station and many small satellites fly. Geostationary orbit is much farther, about 22,000 miles above the equator. A satellite there takes exactly 24 hours to circle Earth, so it seems to hover over one spot. That is why TV dish antennas always point the same direction.

One growing problem is space junk. Old satellites, broken parts, and bits of metal keep orbiting at high speed. Even a fleck of paint can damage a spacecraft because it is moving so fast. Scientists and engineers are trying to figure out how to clean it up before crashes create more junk.

The next time you check the weather, use a map on your phone, or watch a live game from the other side of the world, you are using a satellite.