#moon

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Why the Moon preserves so many impact craters

The Moon lacks the rain, flowing rivers and active plate tectonics that erase many old surface features on Earth. Impact craters can therefore remain visible for extremely long periods. They still change through later impacts and other processes, but the lunar surface preserves a much longer exposed record in many places.

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moon

Why we usually see the same side of the Moon

The Moon rotates once on its axis in approximately the time it takes to orbit Earth once. This synchronous rotation keeps roughly the same hemisphere facing us. The Moon does rotate; if it did not, its journey around Earth would bring different parts of its surface into view over the month.

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eclipses

Why eclipses do not happen every month

The Moon's orbit is tilted by about five degrees relative to Earth's orbital plane around the Sun. Most new and full Moons therefore pass above or below the alignment needed for an eclipse. Eclipses occur when the phase and the Moon's position near an orbital crossing point line up together.

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moon

What causes the Moon's phases

Sunlight normally illuminates about half of the Moon. As the Moon orbits Earth, we see different portions of that illuminated half, producing its phases. An ordinary crescent is therefore not caused by Earth's shadow; that shadow is involved in a lunar eclipse, which requires a more specific alignment.

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