Sky science
Mean Anomaly
Direct answer
Mean Anomaly is a uniformly increasing angular parameter that measures time since periapsis in an ideal Keplerian orbit.
It is the orbit’s linear-in-time phase angle.
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At a glance
- Found in
- Astronomy & Skywatching
- Related
- Argument of Periapsis, True Anomaly, Eccentric Anomaly, Orbital Period
It is the orbit’s linear-in-time phase angle.
A scientific orientation to scale, light, or motion; the article supplies the precise definition.
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The story behind Mean Anomaly
Kepler introduced related auxiliary constructions to connect time with elliptical position.
A one-minute story
The Wandering Stars
How the moving planets were watched, named and found, and what a transit is.
Why Mean Anomaly matters
Mean Anomaly makes orbital timing easier before solving for the actual geometric position.
Mean Anomaly in practice: an example
Mean anomaly advances evenly even while an eccentric planet’s true anomaly does not.
Where readings of Mean Anomaly go wrong
Mean Anomaly is a computational angle, not usually the body’s visible direction.
Sources and editorial method
Research references used for this entry include:
- NASA Science: Orbits and Kepler’s Laws - NASA explanation of orbital ellipses, orbital periods, and Kepler’s laws of planetary motion.
- U.S. Naval Observatory: Astronomical Almanac Glossary - Definitions for astronomical coordinates, time, reference systems, and observable phenomena.
- Source
- The Great Almanac Dictionary
- Category
- Astronomy & Skywatching
- Last updated
- 2026-09-26
Follow uniform orbital phase
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More in Astronomy & Skywatching
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Common questions
What is Mean Anomaly?
Mean Anomaly is a uniformly increasing angular parameter that measures time since periapsis in an ideal Keplerian orbit.
What do people get wrong about Mean Anomaly?
Mean Anomaly is a computational angle, not usually the body’s visible direction.
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