An orbit is a path in space described by a satellite revolving around a larger body, where the motion of the satellite is dominated by the mutual gravitational attraction between it and the larger body. In simpler words, an orbit is the path that something like a planet takes around the Sun, and this path is determined by the attraction between the Sun and the planet.Since the Sun is such a massive object, Earth and all the other planets in the solar system are attracted to it. You may be wondering why the planets don’t fall into the Sun directly. The only factor preventing this from happening is the speed at which the planets are traveling. You observed this in our previous example on Page 4 of the ball which orbited the Earth when you threw it fast enough.
One common misconception about orbits is that when a planet moves around a star, like Earth moves around the Sun, the star stays still. In fact, both Earth and the Sun move in their own circles around the point which is the common center of mass between them (in this example we are ignoring the existence of the other planets). The center of mass is similar to the point at which a see-saw will balance the people sitting on either end, the fulcrum point.
As you can imagine, the center of mass between the Earth and the Sun is much, much closer to the Sun, because the Sun is so much more massive than the Earth. However, in a binary star system, a solar system with two stars, the center of mass for the system is usually right in between the stars. In this case it is easy to see the stars orbit around each other.
To see an orbital simulation click here (requires a Java enabled browser).
