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A full moon is the lunar phase that occurs when the Moon is completely illuminated as seen from the Earth. This occurs when the moon is in opposition to the Sun (when it is on the opposite side of the Earth from the Sun; more precisely, when the ecliptic longitudes of the Sun and Moon differ by 180 degrees). This means that the hemisphere of the Moon that is facing the Earth (the near side) is almost fully illuminated by the Sun and appears round (while the far side is almost completely unilluminated). Lunar eclipses can occur only at full moon, where the Moon's orbit allows it to pass through the Earth's shadow. Lunar eclipses do not occur every month because the Moon usually passes above or below the Earth's shadow (which is mostly restricted to the ecliptic plane). Lunar eclipses can occur only when the full moon occurs near the two nodes of the orbit, either the ascending or descending node. This causes eclipses to only occur about every 6 months, and often 2 weeks before or after a solar eclipse at new moon at the opposite node. The time interval between similar lunar phases—the synodic month—averages about 29.53 days. Therefore, in those lunar calendars in which each month begins on the new moon, the full moon falls on either the 14th or 15th of the lunar month. Because calendar months have a whole number of days, lunar months may be either 29 or 30 days long. ==Characteristics== A full moon is often thought of as an event of a full night's duration. This is somewhat misleading because 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. 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 12 December 2008, the full moon occurred closer to the Earth than it had at any time for the previous 15 years. On 19 March 2011, another super full moon occurred, closer to the Earth than it had at any time for the previous ~18 years. (cycle) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Full moon」の詳細全文を読む スポンサード リンク
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