What is "true anomaly"

n. (context astronomy celestial mechanics English) The angle ''PFC'' formed by ''P'' = the periapsis of a celestial body's elliptical orbit, ''F'' = the focus of that orbit, and ''C'' = the current position of the celestial body.

n. the angular distance of a point in an orbit past the point of periapsis measured in degrees

In celestial mechanics, true anomaly is an angular parameter that defines the position of a body moving along a Keplerian orbit. It is the angle between the direction of periapsis and the current position of the body, as seen from the main focus of the ellipse (the point around which the object orbits).

The true anomaly is usually denoted by the Greek letters or , or the Latin letter .

As shown in the image, the true anomaly is one of three angular parameters ("anomalies") that defines a position along an orbit, the other two being the eccentric anomaly and the mean anomaly. Note that the satellite P orbits around the planet which is at position F.