Knowra True anomaly True anomaly True anomaly is the angle, measured at an orbit’s focus, from the direction of periapsis to an orbiting body’s current position. It specifies the body’s location along its orbit.
Periapsis : The point in an orbit where the orbiting body is closest to its primary. Its direction defines zero true anomaly.
Focus (geometry) : A fixed point used to define conic sections, including the point from which an ellipse’s distances are measured. The orbiting primary lies at a focus, where true anomaly is measured.
Orbit determination : The process of estimating an object's orbit from observations of its position and motion. Estimated orbital states can be expressed using true anomaly.
Argument of periapsis : The angle in an orbital plane from the ascending node to periapsis, measured in the direction of motion. It locates periapsis relative to a reference direction; true anomaly measures position from periapsis.
Kepler's equation : An equation relating mean anomaly, eccentric anomaly, and orbital eccentricity for a Keplerian orbit. Solving it allows true anomaly to be found from elapsed time.
Conic section : A curve formed by intersecting a plane with a cone, including ellipses, parabolas, and hyperbolas. Ideal two-body trajectories follow conic sections with the primary at a focus.
Orbital state vector : A representation of an object's orbital condition using its position and velocity vectors at a given time. True anomaly helps convert orbital elements into position and velocity.
True longitude : An angular coordinate combining an orbit’s orientation with the body’s position along it. Unlike true anomaly, it includes the direction of periapsis within the reference plane.
Vis-viva equation : An equation relating orbital speed, distance from the focus, and the semimajor axis in a Keplerian orbit. Together with true anomaly, it helps determine distance and speed along an orbit.
Eccentricity (orbit) : A dimensionless measure of an orbit’s departure from circular shape. Eccentricity determines how angle maps to distance along an orbit.
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