If the moon is completing the rotation of the earth every month shouldn’t eclipse be a monthly phenomenon
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The earth moves around the sun in a nearly circular orbit. You can imagine a circular flat plate that extends from the sun with the earth running around its perimeter.
The moon moves around the earth in a similar fashion and you can imagine a similar plate extending from the earth.
The KEY point is that those 2 plates are not coincident because the orbit of the moon is at an angle to the orbit of the earth. (NOT related to the tilt of the earth’s axis btw).
Eclipses only happen when all 3 bodies are in a straight line (in 3D). In most cases when the moon is full (i.e. in a straight line in 2D) it lies above or below the shadow of the earth (which will be on the ‘plate’ delineating the earth’s orbit)
It should also be noted that by the geometry of the sizes of the bodies and their orbits the shadow of the earth at the distance of the moon is not very much bigger than the moon itself. That is why a) Lunar eclipses don’t last long, and b) why partial eclipses are much more common than total.
The same applies for when the moon is between the earth and sun – creating a solar eclipse.
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