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The Moon's Holiday Gift
12.20.10
 
The December holiday sky show doesn't stop with the Geminid meteor shower. In the very early morning of December 21 (or late night of December 20, depending on your time zone), a total lunar eclipse will make a dramatically colorful appearance -- from bright orange to blood red to dark brown and perhaps gray. The next total lunar eclipse will begin when the moon moves into Earth's penumbral shadow on December 21, 2010 at 5:29 UTC.

A lunar eclipse occurs when the moon passes behind Earth, into Earth's shadow. This type of eclipse occurs when the sun, Earth, and moon are aligned exactly, or very closely so, with Earth in the middle. Hence, there is always a full moon the night of a lunar eclipse. The type and length of an eclipse depend upon the moon's location in its orbit relative to the Earth and sun.

The last lunar eclipse of 2010 is especially well placed for observers throughout North America. The eclipse occurs as the moon passes through the northern portion of Earth's shadow, just four days before perigee, when the moon is closest to Earth.

The shadow of the Earth can be divided into two distinctive parts: penumbra and umbra. As a result of the sun's large angular size, solar illumination is only partially blocked in the outer portion of the Earth's shadow, the penumbra, which results in a very subtle dimming of moonlight. The penumbral start time of a lunar eclipse (Dec. 21, 5:29 UT) begins before you will see the umbral shadow touching the moon. An observer on Earth sees only a vary faint reduction in brightness in this phase and may notice nothing. The obvious shadowing begins with the umbral phase of the eclipse. Within the umbra, the moon will appear dimmest.

Unlike solar eclipses which can last for only a maximum of about seven minutes, the umbral (darkest) portion of a lunar eclipse can last for more than an hour. The partial phase of this eclipse, when the moon begins moving into the umbral part of Earth's shadow, begins at 6:33 UT. To see the darkest portion of this last lunar eclipse of 2010, begin looking at 7:41 U.T. Consult the table below for local time conversions.

  Partial Phase Begins Moon Enters Umbra Mid-Eclipse Moon Leaves Umbra
EST Dec. 21, 1:33 a.m. Dec. 21, 2:41 a.m. Dec. 21, 3:17 a.m. Dec. 21, 3:53 a.m.
CST Dec. 21, 12:33 a.m. Dec. 21, 1:41 a.m. Dec. 21, 2:17 a.m. Dec. 21, 2:53 a.m.
MST Dec. 20, 11:33 p.m. Dec. 21, 12:41 a.m. Dec. 21, 1:17 a.m. Dec. 21, 1:53 a.m.
PST Dec. 20, 10:33 p.m. Dec. 20, 11:41 p.m. Dec. 21, 12:17 a.m. Dec. 21, 12:53 a.m.


For more detailed information, see Fred Espenak's page:
http://www.mreclipse.com/LEdata/TLE2010Dec21/TLE2010Dec21.html