On Oct. 4, 1957, the Soviet Union launched Sputnik I, the world's first artificial satellite. It was approximately the size of a beach ball and weighed almost 184 pounds. It orbited the Earth in only 98 minutes. It marked a new era in political, military, technological and scientific developments, beginning the space age and the U.S.-U.S.S.R space race.
Image Credit: NASA
A satellite is launched into orbit, which means that it goes around the earth. Newton had an explanation that tells why satellites, like the moon, can stay in orbit. Picture a yo-yo doing the “around the world” trick, where the yo-yo makes a big circle around your hand where the string is connected. As the yo-yo falls around your hand it is constantly being pulled back in by the string, making the yo-yo continue in a loop. Basically, according to Newton’s idea of gravity, a satellite travels around the earth because the gravitational pull from the earth yanks on the satellite just enough that as the satellite falls it makes a curve, making the satellite travel in a curved path around the earth.
Einstein had another explanation. As Einstein saw it there are four dimensions that make up the fabric of space. We call this fabric space-time. Whenever there is an object with mass, such as our earth, in this fabric it creates a gravity well, which, as the name implies, is like a dip in space-time. When objects that have mass are placed in motion around an object of larger mass, the smaller object will orbit the more massive object by following the curvature of space-time created by the gravity well of the more massive object.
Gravity - From Newton to Einstein - The Elegant Universe
NASA Image Gallery - Sputnik
The History of Sputnik