#rotation

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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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launches

Why many launches head east

Earth's rotation already gives a launch site eastward speed. A rocket heading into a suitable eastward orbit can use that initial motion, reducing the extra speed it must supply. The benefit is greatest near the equator, but the destination orbit and safe flight path can make another direction necessary.

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