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The Once and Future Moon

Earth’s Nightlight

26 Jun 2013, 13:46 UTC
Earth’s Nightlight
(200 words excerpt, click title or image to see full post)

The Moon's motions have a significant impact on life on Earth.

This month's "Super Moon" drew worldwide attention
As a naturally orbiting object, the Moon orbits Earth in an elliptical path, with the center of the Earth at one focus – more precisely, both Earth and Moon orbit each other around what it called the barycenter, the imaginary point about 1800 km below the surface of the Earth that constitutes their mutual center of gravity. Since the Moon is only about one percent the mass of Earth, the barycenter is much closer to the center of Earth than it is to the center of the Moon.
When the Moon comes closest to Earth in its elliptical orbit it is said to be at perigee. If the Sun, Earth and Moon come into alignment along a straight-line, a condition occurs that astronomers perversely have named syzygy (a great word to keep in your hip pocket the next time you play Scrabble, though you’ll need a blank to get there). Syzygy (alignment) is not the same as perigee (the closest approach of Moon to Earth) but on the occasion when syzygy and perigee coincide, we have what’s called a “Super Moon.”
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