Noun

Singular orbit

Plural orbits

orbit (plural orbits)

1. A circular or elliptical path of one object around another object.

   The Moon's orbit around the Earth takes nearly one month to complete.

2. A sphere of influence; an area of control.

   In the post WWII era, several eastern European countries came into the orbit of the Soviet Union.

3. The course of one's usual progression, or the extent of one's typical range.

   The convenience store was a heavily travelled point in her daily orbit, as she purchased both cigarettes and lottery tickets there.

4. (anatomy) The bony cavity containing the eyeball; the eye socket.
5. (physics) The path an electron takes around an atom's nucleus
6. (mathematics) A collection of points related by the evolution function of a dynamical system.

In physics, an orbit is the gravitationally curved path of one object around a point or another body, for example the gravitational orbit of a planet around a star.

Historically, the apparent motions of the planets were first understood geometrically (and without regard to gravity) in terms of epicycles, which are the sums of numerous circular motions. Theories of this kind predicted paths of the planets moderately well, until Johannes Kepler was able to show that the motion of the planets were in fact (at least approximately) elliptical motions. In Isaac Newton's Principia (1687), Newton derived the relationships now known as Kepler's laws of planetary motion from a force-based theory of universal gravitation. Albert Einstein's later general theory of relativity was able to account for gravity as due to curvature of space-time, with orbits following geodesics.