Scheme for deriving the relation between the true and mean anomaly. C is the common centre of the ellipse and the auxiliary circle. S is the focus of the ellipse. The semimajor and semiminor axes are CA = a and CB = b, respectively. The orbital postion of the object is P, its perpendicular projection on the semimiajor axis is R, and the intersection of PR and the auxiliary circle is Q. |SP|=r and CS = ae, where e is the eccentricity of ellipse. The angles ∠QCA and ∠PSA are the eccentric and the true anomaly, respectively. The radius of the auxiliary circle equals the orbital semimajor axis.