Hodograph Movie

The ellipse is an object's orbit about the sun, the sun is at the ellipse focus at the foot of the position vector.

A red vector of constant length stays at right angles to the position vector.

A blue vector of constant length stays vertical.

The sum of the blue and red vectors is the velocity vector.

Note that the velocity vector is largest (fastest) when the object is closest to the sun and is smallest (slowest) when the object is furthest from the sun.

This movie was inspired by the book Orbital Mechanics by John Prussing and Bruce Conway