Why does a solar eclipse move from west to east, while the sun moves from east to west?
Asked by: David Weissenberger
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
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
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