Circular orbit

In astronomy, a circular orbit refers to an object (such as a planet or a star) which orbits around a central body in a fixed, circular motion. This motion follows Kepler's Laws. A circular orbit occurs when the eccentricity of its orbit is equal to 0.
Objects with a circular orbit are uncommon. The Moon moves in an elliptical orbit around the Earth, and the planets move in an elliptical orbit around the Sun.
Other types of motion in astronomy include elliptical orbit, parabolic trajectory, and hyperbolic trajectory.