EQUATION OF THE CENTRE  , in astronomy, the angular distance, measured around the centre of motion, by which a planet moving in an ellipse deviates from the mean position which it would occupy if it moved uniformly . Its amount is the correction which must be applied positively or negatively to the mean anomaly in order to obtain the true anomaly . It arises from the ellipticity of the orbit, is zero at pericentre and apocentre, and reaches its greatest amount nearly midway between these points .