Equal Areas, Equal Times

The gold ellipse shows the path. It can't tell you when a ball will reach any point on it. Let's put a clock on it.

Kepler's area rule

A ball on an ellipse doesn't move at a steady speed. It races past the planet and crawls at the far end. Kepler found the rule. Draw a line from the planet to the ball, and that line sweeps out equal areas in equal times.

Near the planet the line is short, so the ball has to cover a lot of ground to sweep its share. Far away the line is long, so a little movement does it.