Why does the passage call the Earth a satellite?

A satellite is anything that orbits a planet or a star. By that definition the Earth is a satellite, because it orbits the Sun, and the Moon is a satellite of the Earth. These are natural satellites. Thousands of others have been made by people.

America's first man-made satellite, Explorer 1, was launched in 1958. Today's satellites come in many shapes and sizes, but nearly all have two parts in common: an antenna, for sending and receiving information, and a source of power, usually solar panels or batteries.

A satellite stays in orbit because of a balance between its speed and the pull of gravity. Without that balance, it would either drift off into space or crash back down.

Satellites do many jobs. Some take pictures of the Earth's land, air and water, helping scientists to follow the weather and to track hurricanes, wildfires and volcanoes. More than 30 satellites make up the GPS system that tells phones and cars where they are. Others look out into space, at black holes and distant galaxies, and many carry television signals and phone calls around the world.

Two common kinds of orbit are geostationary, in which a satellite stays above the same spot on the equator, and polar, in which it passes over the North and South Poles.