Editing Lunar phase (section)

==Other observational phenomena==
===Lunar libration===
[[File:Lunar libration with phase Oct 2007 (continuous loop).gif|thumb|right|240px|Animation showing progression of the Moon's phases.]]

As seen from Earth, the Moon's eccentric orbit makes it both slightly change its apparent size, and to be seen from slightly different angles.

The effect is subtle to the naked eye, from night to night, yet somewhat obvious in time-lapse photography.

Lunar libration causes part of the back side of the Moon to be visible to a terrestrial observer some of the time. Because of this, around 59% of the Moon's surface has been imaged from the ground.
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=== Effect of parallax ===
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The [[Earth]] subtends an angle of about two degrees when seen from the Moon. This means that an observer on Earth who sees the Moon when it is close to the eastern horizon sees it from an angle that is about 2 degrees different from the line of sight of an observer who sees the Moon on the [[West|western horizon]]. The Moon moves about 12 degrees around its orbit per day, so, if these observers were stationary, they would see the phases of the Moon at times that differ by about one-sixth of a day, or 4 hours. But in reality, the observers are on the surface of the rotating Earth, so someone who sees the Moon on the [[East|eastern horizon]] at one moment sees it on the western horizon about 12 hours later. This adds an oscillation to the apparent progression of the lunar phases. They appear to occur more slowly when the Moon is high in the sky than when it is below the horizon. The Moon appears to move jerkily, and the phases do the same. The amplitude of this oscillation is never more than about four hours, which is a small fraction of a [[month]]. It does not have any obvious effect on the appearance of the Moon. It does however affect accurate calculations of the times of lunar phases.

=== Earthshine ===
[[File:Lumiere cendrée (12273290216).jpg|thumb|right|An [[exposure (photography)|overexposed]] photograph of a crescent Moon reveals earthshine and stars.]]
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When the Moon (seen from Earth) is a thin [[crescent]], Earth (as viewed from the Moon) is almost fully lit by the Sun. Often, the dark side of the Moon is dimly illuminated by indirect sunlight reflected from Earth, but is bright enough to be easily visible from Earth. This phenomenon is called [[earthlight (astronomy)|earthshine]], sometimes picturesquely described as "the old moon in the new moon's arms" or "the new moon in the old moon's arms".
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