True anomaly

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). 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 ν or θ, or the Latin letter f. As shown in the image, the true anomaly f 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. For elliptic orbits, the true anomaly ν can be calculated from orbital state vectors as: