Today’s Wonder of the Day was inspired by sophie. sophie Wonders, “Why are satellites helpful?” Thanks for WONDERing with us, sophie!

Without these things, our daily lives would look much different. Some of us couldn't watch television. Some of us couldn't figure out how to navigate from one place to another when traveling. Some of us could be endangered by bad weather that we didn't know was coming. What are we talking about? Satellites, of course!

Satellites are any objects that revolve around (orbit) another object in space. Some satellites are natural, while others are artificial (man-made). The moon is an example of a natural satellite that orbits the Earth. We're going to focus, though, on the man-made satellites.

Artificial satellites are machines that humans launch into orbit, usually around the Earth. Artificial satellites can be sent to orbit other planets, too. For example, there are currently satellites orbiting the Moon, the Sun, and several other planets, including Mercury, Venus, Mars, and Saturn.

The Soviet Union launched the first artificial satellite — Sputnik 1 — on October 4, 1957. The United States launched its first artificial satellite — Explorer 1 — about four months later.

Since that time, over 2,500 satellites have been launched into space. Would you have ever guessed there are that many satellites up there in the sky, traveling around the Earth over and over again?

What in the world do they do up there? Why do we need so many of them? Artificial satellites are used for all sorts of purposes. Satellites like the Hubble Space Telescope, the International Space Station, and the Russian Mir space station help scientists explore space in new and exciting ways.

Communications satellites help us communicate with people all over the world. Weather satellites help us observe the Earth from space to help predict weather patterns. Radio and television satellites beam our favorite songs, movies, and television shows to Earth for us to enjoy.

There's even a group of 27 satellites that make up the Global Positioning System (GPS). Without these satellites, we couldn't use GPS devices to find our way while traveling.

If you're wondering how that many satellites stay in orbit without bumping into each other, just remember that space is very…well…spacious! Compared to our measurements on Earth, the size of space seems infinite.

Even though there's a lot of room in space, satellites are launched into orbits at different distances from Earth. Some may be as close as 150 miles above Earth, while others may be as far away as 20,000 miles or more.

Most artificial satellites orbit within 500 miles of Earth or what scientists call low-Earth orbit. These satellites have to travel very fast — about 17,000 miles per hour — to avoid being sucked back into Earth's atmosphere.

Sooner or later, though, the force of gravity will pull all objects, including artificial satellites, back to Earth. When satellites quit working, they become orbiting “space junk" until gravity pulls them back to Earth. Although at least one piece of space junk returns to Earth every day, it's rare that anyone ever notices. So no need to worry that the sky is falling!

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