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Sky Sights: December's Total Lunar Eclipse

Mercury Autumn 2010 Table of Contents

by Paul Deans

The highlight of the month is the total eclipse of the Moon during the night of December 20/21. Although the eclipse is not central, the total phase still lasts 72 minutes.

At the instant of greatest eclipse, the Moon is almost directly overhead for observers in southern California. The entire event is visible from North America and western South America. Observers on South America's east coast miss the late stages of the eclipse because they occur after moonset. Likewise, much of Europe and Africa experience moonset while the eclipse is in progress, though northern Scandinavians can catch the entire event. For observers in eastern Asia, the Moon rises in eclipse. None of the eclipse is visible from south and east Africa, the Middle East, or South Asia.

Listed below are some of the key events, and the times they will occur, during December's total lunar eclipse. Note that UT is Universal Time (sometimes called Greenwich Mean Time or GMT). Eastern Time is UT – 5 hours; Central is UT – 6; Mountain is UT – 7; and Pacific Time is UT – 8 hours. The eclipse is also visible in its entirety from Alaska (local time is UT – 9 hours) and Hawaii (UT – 10 hours), but be aware that most of the eclipse occurs on the 20th in these two regions.

December 21, 2010


Eastern time

Pacific time

Penumbral Eclipse Begins


12:29 am

9:29 pm on the 20th

Partial Eclipse Begins


1:33 am

10:33 pm on the 20th

Total Eclipse Begins


2:41 am

11:41 pm on the 20th

Greatest Eclipse


3:17 am

12:17 am

Total Eclipse Ends


4:53 am

12:53 am

Partial Eclipse Ends


5:01 am

2:01 am

Penumbral Eclipse Ends


6:04 am

3:04 am

While the eclipse officially begins when the Moon enters the penumbra (Earth’s faint, outer shadow), it’s an event that’s impossible to see. The real “action” begins when the Moon enters Earth’s dark shadow -- the umbra. As the umbra covers the Moon, notice that Luna doesn’t become completely dark and invisible. Light bent through Earth’s atmosphere still reaches the shadowed Moon and gives it a dull brown or reddish glow. (Since the Moon passes through a large range of umbral depths during totality, its appearance will change dramatically with time.) The color and darkness of the totally eclipsed Moon depends on how murky Earth’s atmosphere is, and that depends on such things as how much cloud cover, storm activity, and human pollution there is around the globe, and even how recently (and vigorously) volcanoes have erupted.

eclipse chart

So set your alarm clock (if necessary), and don’t miss this lovely spectacle. A lunar eclipse is one celestial event that’s leisurely and doesn’t require a telescope to observe -- your eyes are all you need (though binoculars are a nice addition).

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