Why does a solar eclipse move from west to east, while the sun moves from east to west?

Asked by: David Weissenberger

Answer

The Moon orbits the Earth from west to east. If you want to verify this, watch Moonrise on successive nights and you'll see that it rises later each day as the Earth's rotation needs more time to 'catch up' with the Moon in its orbit.

The Moon's orbital velocity is about 1 km/sec, so its shadow travels at that same velocity. While the Earth's rotation also proceeds from west to east, the FASTEST motion generated by that rotation is at the equator and works out to less than .5 km/sec. So the Moon's shadow moves eastward at a velocity greater than the Earth's rotational velocity at any location or time, causing it to travel west to east across the Earth's surface.
Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor