# anomaly

Fig 1. The true anomaly of point *P* is the angle *f*. The center of the ellipse is point *C*, and the focus is point *F*.

The anomaly is an angle that gives the position of an object in an elliptical orbit at any given time.

The **true anomaly** (Fig 1)is the angle
between the periapsis of an orbit and
the object's current orbital position, measured from the body being orbited
and in the direction of orbital motion.

The **mean anomaly** is what the true anomaly would be if the object orbited in a perfect circle
at constant speed. The mean anomaly is 0° at periapsis and 180°
at apoapsis, just as for the true anomaly, but at other points along the
orbit the values of the mean and true anomalies differ. The mean anomaly
at a given time is often used as an orbital element.

The **eccentric
anomaly** is an angle related to both the true anomaly and the mean
anomaly that is encountered when solving Kepler's
equation.