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.