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Make sure to circle May 15 on your calendar, the night that stages a total eclipse of the Moon. The show begins a hair's-breadth after 10 p.m. (Eastern Daylight Time), when the Moon makes its initial plunge into the Earth's dark shadow -- "umbra" in astronomical jargon. The Moon, taking one hour and 11 minutes to enter into the umbra completely, becomes totally eclipsed by 11:13 p.m. Totality lasts for some 53 minutes, and ends at 12:06 a.m. After the total eclipse, the Moon remains partially eclipsed for another hour and 11 minutes, finally exiting the Earth's shadow by 1:17 a.m.
Mid eclipse, or the eclipse's deepest moment, comes at 11:40 p.m. Even at this dark hour, the northern (top) part of the Moon will likely look lighter than the southern (bottom) part, which passes more closely to, though above, the center of the Earth's shadow. (See map.)*
If the Moon were to cross the central portion of shadow, as it did on July 16, 2000, the total eclipse would last for one hour and 47 minutes -- or about twice as long. On the other hand, if the Moon were to pass near the shadow's edge, as it will on April 4, 2015, the total eclipse would last only 12 minutes.
A lunar eclipse can only happen at full Moon. If the Moon orbited the Earth on the same plane that the Earth orbited the Sun, a total eclipse would occur every month at full Moon. But the geometry is such that the full Moon usually eludes the Earth's shadow by orbiting above it or beneath it.
The plane of the Moon's orbit is tilted about 5 degrees to the "ecliptic" -- the plane of the Earth's orbit around the Sun. For half of the month the Moon travels north of the ecliptic and the other half it travels south of it. But twice a month, when the Moon crosses the plane of the ecliptic, an eclipse is not only possible but inevitable -- if, at this time, the Moon is either new or full.
The eclipsed Moon resides in the constellation of Libra. At mid eclipse, the Moon shows you where the Sun will be shining amongst the stars on November 17, or six calendar months henceforth.
* All maps used in this article courtesy of Fred Espenack, NASA, Goodard Space Flight Center
|May 16 Eclipse Map||Saros Eclipse Cycle||Keith's Moon Page|
|Eclipse Predictions by Fred Espenak, NASA/GSFC|