Anomaly (astronomy)

In astronomy and celestial mechanics, the anomaly is the current angle of a celestial body to the periapsis of its orbital ellipse , the point closest to the center:

• as a true anomaly measured at the center of gravity of the system (the focal point of the ellipse):

  gives - as a solution of the Kepler equation - the movement on an ideal elliptical path, see Kepler equation: True anomaly ,

• as an eccentric anomaly in the circumscribed circle :

  it serves in particular to solve the Kepler problem, see Kepler equation: eccentric anomaly ,

• as a mean anomaly in a fictitious uniform movement :

  the mean anomaly gives the orbit linearly in time as a first approximation, see Kepler equation: mean anomaly ,

for all three quantities see Kepler equation .

Because the anomaly represents the true orbital period (relative, in a two-body system ), the orbital time measured from periapsis to periapsis is called "anomalistic". These are in particular:

• anomalistic year (between two perihelion passages of the earth), 365 days and 6:13:53 hours
• anomalous month (between two perigee passages of the moon), 27.55 days.

literature

• Andreas Guthmann: Introduction to celestial mechanics and ephemeris calculus. 2nd Edition. Spectrum Academic Publishing House, 2000, ISBN 3-8274-0574-2 .