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abstraction > mathematical concept > number > quantity > orbital quantity > orbital element > eccentricity

eccentricity (e)
subject			fact

eccentricity	has symbol e
	has definition An orbital element representing the eccentricity of the elliptical orbit
	has definition In astronomy, the extent to which an elliptical orbit departs from a circular one. It is usually expressed as a decimal fraction, regarding a circle as having an eccentricity of 0.
	has definition A measure of how round or elliptical an orbit is. A perfect circle has an eccentricity of 0 percent, and an extremely elliptical orbit has an eccentricity of just under 100 percent. The Sun has an orbital eccentricity of 6 percent, which means that at perigalacticon the Sun is 6 percent closer to the Galactic center than its mean distance and at apogalacticon the Sun is 6 percent farther from the Galactic center than its mean distance.
	has definition A parameter that specifies the shape of a conic section; one of the standard elements used to describe an elliptic orbit. (See elements, orbital.)
	has definition The amount by which the elliptical orbit deviates from circularity: e = c/a, where c is the distance from the center to a focus and a is the semimajor axis.
	is an instance of orbital element
orbital element	is required to define the size, shape, and orientation of an orbit in space
	see also mean element
	see also osculating element
quantity	has unit
number	has value