True Anomaly
The angular position of a satellite along its orbital path, measured from periapsis as the angle between the periapsis direction and the satellite's current position.
Explanation
True anomaly (ν, nu) is the sixth Keplerian orbital element, describing where a satellite is at a specific time within its orbit. It is measured in degrees from 0 to 360, with 0 degrees at periapsis and 180 degrees at apoapsis. True anomaly changes most rapidly at periapsis (where the satellite moves fastest) and most slowly at apoapsis (where it moves slowest), following Kepler's second law of equal areas. Along with the epoch time, true anomaly allows the calculation of a satellite's exact position. In TLE data, mean anomaly at epoch is provided instead of true anomaly, which is then converted to true anomaly through Kepler's equation. True anomaly is essential for conjunction assessment, ground station pass planning, and spacecraft operations.
Why It Matters
True anomaly converts orbital parameters into actual position. Without it, you know the shape and orientation of an orbit but not where the satellite is right now.
Concept Map
How True Anomaly connects to other glossary terms:
Frequently Asked Questions
How is true anomaly different from mean anomaly?
Mean anomaly assumes constant angular velocity for a simple calculation. True anomaly is the actual angular position, accounting for Kepler's second law (faster at perigee, slower at apogee).
What is true anomaly at perigee?
True anomaly is 0 degrees at perigee and 180 degrees at apogee.
Sources
Last updated: July 1, 2026