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Graph of asteroid semimajor axis versus eccentricity
Graph of asteroid semimajor axis versus eccentricity Semimajor axis, on the X axis and measured in astronomical units, describes an object's distance from the Sun. It is the longest radius of an object's elliptical orbit. Eccentricity, on the Y axis, is a dimensionless parameter that describes how elliptical an orbit is; an eccentricity of 0 describes a circular orbit, and an eccentricity of 1 describes a parabolic orbit. Minor Planet Center