deviation from the common rule; an irregularity; anything anomalous.-the angular distance of a planet from its perihelion, as seen from the sun. this is the true anomaly. the eccentric anomaly is a corresponding angle at the center of the elliptic orbit of the planet. the mean anomaly is what the anomaly would be if the planet's angular motion were uniform.-the angle measuring apparent irregularities in the motion of a planet.-any deviation from the essential characteristics of a specific type.