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Night of the Red Moon, 2010

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Moon in Lunar Eclipse

Moon during a Lunar eclipse.

Credit: Oliver Stein


For a few hours on the night of Dec. 20-21, the attention of tens of millions of people will be drawn skyward, where there will hang a mottled, coppery globe—our moon—completely immersed for a while in the long, tapering cone of shadow cast out into space by our earth. If the weather is clear, favorably placed sky watchers will have a view of one of nature's most beautiful spectacles: A Total Eclipse of the moon.

Unlike a total eclipse of the sun, which often requires a long journey to the path of totality, those of the moon can usually be observed from one's own backyard. The passage of the moon through the Earth's shadow is equally visible from all places within the hemisphere where the moon is above the horizon.

The total phase of the upcoming event will be visible across all of North and South America, as well as the northern and western part of Europe, and a small part of northeast Asia including Korea and much of Japan. Totality will also be visible in its entirety from the North Island of New Zealand and Hawaii—a potential viewing audience of about 1.5 billion people. This will be the first opportunity from any place on earth to see the moon undergo a total eclipse in 34 months.

Stages of the Eclipse

There is nothing complicated about how to view this celestial spectacle. Unlike an eclipse of the sun which necessitates special viewing precautions in order to avoid eye damage, an eclipse of the moon is perfectly safe to watch. All you'll need to watch are your eyes, but binoculars or a telescope will give a much nicer view.

Total Lunar Eclipse Dec 2012

Stages of the total lunar eclipse of December 2010.

Credit Fred Espenak/NASA.


The eclipse will actually begin when the moon enters the faint outer portion, or penumbra, of the earth's shadow a little over an hour before it begins moving into the umbra. The penumbra, however, is all but invisible to the eye until the moon becomes deeply immersed in it. Sharp-eyed viewers may get their first glimpse of the penumbra as a faint "smudge" on the left part of the moon's disk at or around 1:15 A.M. Eastern Time or 10:15 P.M. Pacific Time (on Dec. 20).

The most noticeable part of this eclipse will come when the moon begins to enter the earth’s dark inner shadow (called the umbra). A small scallop of darkness will begin to appear on the moon's left edge at 1:33 A.M. Eastern Time or 10:33 P.M. Pacific Time (on Dec. 20).

The moon is expected to take 3 hours and 28 minutes to pass completely through the umbra.

The total phase of the eclipse will last 72 minutes beginning at 2:41 A.M. Eastern Time or 11:41 P.M. Pacific Time (on Dec. 20). At the moment of mid-totality (3:17 A.M. Eastern Time/12:18 A.M. Pacific Time), the moon will stand directly overhead from a point in the North Pacific Ocean about 800 miles (1,300 km) west of La Paz, Mexico.

The moon will pass entirely out of the earth's umbra at 5:01 A.M. Eastern Time/2:01 A.M. Pacific Time and the last evidence of the penumbra should vanish, about 15 or 20 minutes later.

Only the Shadow Knows the Moon’s Color

Although astronomers do not expect to gain new astronomical insights from the eclipse, lunar eclipses vividly reflect the overall state of the earth’s atmosphere. Under normal weather and atmospheric conditions, as the moon slides into the shadow of the earth, its normal yellow-white color changes into a still-visible but dull coppery-red at the height of the eclipse. Since the earth's shadow is cone-shaped and extends out into space for some 844,000 miles (1,358,000 km), sunlight will be strained through a sort of “double sunset,” all around the rim of the earth, into its shadow and then onto the moon.

However, because of the recent eruptions of the Mt. Eyjafjallajökull volcano in Iceland last spring and the Mt. Merapi volcano in Indonesia in October, one and possibly two clouds of ash and dust might be currently floating high above the Earth. As a result, the moon may appear darker than usual during this eclipse; during totality, parts of the moon might even become black and invisible.

Or . . . the moon might wear its normal eclipse cloak of a deep red or a coppery-hue or take on still other colors (orange, chocolate brown or gray). Color possibilities are unpredictable and that it is impossible to tell exactly how much light the earth’s atmosphere will refract as its shadow creeps across the moon. Cloud cover and other atmospheric conditions may also affect the visibility and coloration of the Moon.

In short: we’ll all just have to wait for eclipse night and see what actually happens.

At mid-totality, from rural locations far from city lights, the darkness of the sky is impressive. Faint stars and the Milky Way will appear, and the surrounding landscape will take on a somber hue. As totality ends, the eastern edge of the moon begins to emerge from the umbra, and the sequence of events repeats in reverse order until the spectacle is over.

Past and Future

The last total lunar eclipse occurred on Feb. 20-21, 2008 and was visible from most of the Americas, as well as Europe, much of Africa and western Asia. In 2011 there will be two total lunar eclipses. The first, on Jun. 15 will be visible primarily from the Eastern Hemisphere and will have an unusually long duration of totality lasting one hour and 40 minutes. Another total lunar eclipse will occur on Dec. 10 and will be visible over the western half of North America before moonset. For the next total lunar eclipse that will be visible across all of North America, we must wait until Apr. 14-15, 2014.

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