# mean motion

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## mean motion

The constant angular speed that is required for a celestial body to complete one revolution of an (undisturbed) elliptical orbit of a specified semimajor axis.## Mean Motion

(religion, spiritualism, and occult)Because celestial bodies move in elliptical orbits, their speed varies depending upon their location. Mean motion refers to their average speed.

## Mean Motion

an element, or parameter, of the orbit of a celestial body that characterizes the dimensions of the orbit. The relation between the mean motion and the semimajor axis of the orbit is given by Kepler’s third law: the larger the semimajor axis, the more slowly the body, on the average, moves in its orbit. (*See*ORBIT OF A CELESTIAL BODY.)

## mean motion

[′mēn ′mō·shən] (astronomy)

The speed which a planet or its satellite would have if it were moving in a circular orbit with radius equal to its distance from the sun or a central planet with a period equal to its actual period.