Aurie swept oot per unit time bi an object in an elliptical orbit (grey) an bi an imaginary object in a circular orbit (reid) which completes its orbit in the same period o time. Baith sweep oot equal auries in equal times, but the angular rate o sweep varies for the elliptical orbit an is constant for the circular orbit. Shawn are mean anomaly an true anomaly for twa units o time.

In celestial mechanics, the mean anomaly is an angle uised in calculatin the poseetion o a bouk in an elliptical orbit in the clessical twa-bouk problem.