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A full Lunar Cycle (Lunation)
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Da "Astronomy: Picture of the Day", del 13 Novembre 2005:"Our Moon's appearance changes nightly. This time-lapse sequence shows what our Moon looks like during a lunation, such as a complete Lunar Cycle.
As the Moon orbits the Earth, the half illuminated by the Sun first becomes increasingly visible, then decreasingly visible. The Moon always keeps the same face toward the Earth and its apparent size changes slightly, though, and a slight wobble called "libration" is discernable as it progresses along its elliptical orbit.
During the cycle, sunlight reflects from the Moon at different angles and so illuminates different features differently. A full lunation takes about 29,5 days, such as just under a month (moon-th)".
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(Dettagli)
