Anomaly

Anomaly (Gr. anomalía, 'irregularity'), the angle measured at the sun between a planet in any point of its orbit and the last perihelion. It is so called because the first irregularities of planetary motion were discovered in the discrepancy between the actual and computed distance. The anomaly was formerly measured from the aphelion, the opposite point of the ellipse; but from the fact that the aphelia of most of the comets lie beyond the range of observation, the perihelion is now taken as the point of departure for all planetary bodies.