Area swept out per unit time      by an object in an elliptical orbit, and      by an imaginary object in a circular orbit (with the same orbital period). Both sweep out equal areas in equal times, but the angular rate of sweep varies for the elliptical orbit and is constant for the circular orbit. Shown are mean anomaly and true anomaly for two units of time.  (Note that for visual simplicity, a nonoverlapping circular orbit is diagrammed, thus this circular orbit with same orbital period is Not shown in true scale with this elliptical orbit. For scale to be true for orbits of equal period, diameter of circle must equal major axis of ellipse, thus these orbits must intersect at two points. Visually simplified, but Theoretically confusing.)