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Hopefully you had the time, and clear skies, to watch the lunar eclipse that occurred this past Sunday night. The moon was at its perigee, the point in the orbit at which it is nearest to the earth. So it was about 15% brighter than at other times. All this talk about the moon and you invariably hear the expression “the dark side of the moon”.
Dark Side of the Moon
The far side of the moon is not dark. During a ‘new moon’, the moon is between the Earth and the Sun, and so the side we know is totally dark and the far side will be bright. When the moon is opposite from the Sun, a full moon, the side we know will be totally bright, and the far side will be dark.
Why do we only see one side of the Moon?
We all know that the Earth rotates on its own axis, so theoretically, the Moon should also do the same, allowing us to get a full picture of the planetoid. Why are we limited to seeing only 50 percent? It turns out that the speed at which the Moon rotates has led to this particular phenomenon. Millions of years ago, the Moon spun at a much faster pace than it does now. However, the gravitational influence of the Earth has gradually acted upon the Moon to slow its rotation down, in the same way that the much smaller gravitational influence of the Moon acts upon the Earth to create tides. This influence slowed the rotational period of the Moon to match that of its orbit – about 27.3 days – and it is now “locked in” to this period.