Characteristics
A full moon is often thought of as an event of a full night's duration. This is somewhat misleading, as the Moon seen from Earth is continuously becoming larger or smaller (though much too slowly to notice with the naked eye). Its absolute maximum size occurs at the moment expansion has stopped, and when graphed, its tangent slope is zero. For any given location, about half of these absolute maximum full moons will be potentially visible, as the other half occur during the day, when the full moon is below the horizon. Many almanacs list full moons not just by date, but by their exact time as well, usually in Coordinated Universal Time (UTC). Typical monthly calendars that include phases of the moon may be off by one day if intended for use in a different time zone.
Full moons are generally a poor time to conduct astronomical observations, since the bright reflected sunlight from the moon overwhelms the dimmer light from stars.
On 21 December 2008 the full moon occurred closer to the Earth than it has done at any time for the past 15 years.
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