Lunar eclipse, winter solstice to coincide
This year's winter solstice on Tuesday will fall on the same day as a full lunar eclipse for the first time in 372 years.
The rare, 72-minute lunar eclipse — when the sun, the Earth and the moon align — will begin in the early morning hours on Dec. 21 in North America, and should cast an amber glow on snowy landscapes, said NASA.
Why moon will appear red
If you were to stand on the moon's surface looking up at the sky, you would see Earth hanging above, nightside down, and completely hiding the sun behind it.
Rather than being completely dark, the Earth's rim would appear as if it were on fire. Around its circumference, you would be seeing every sunrise and every sunset in the world at the same time.
This surrounding light will actually beam right into Earth's shadow, giving it a rusty glow.
From the Earth, the moon would appear as a giant red orb because the only sunlight visible is refracted through the Earth's atmosphere.
The moon will pass through the darkest part of the Earth's shadow.
Tuesday marks the first day of winter in the northern hemisphere, and the winter solstice begins in the evening at 6:38 p.m. ET, which is 8:08 p.m. NT, 7:38 p.m. AT, 5:38 p.m. CT, 4:38 p.m. MT, and 3:38 p.m. PT.
Scientists said the last time a full lunar eclipse coincided with the winter solstice was in AD 1638. NASA forecasts that at 1:33 a.m. ET on Tuesday, "Earth's shadow will appear as a dark red bite at the edge of the lunar disk."
After roughly an hour, that "bite" will eventually grow to cover the whole moon. That stage, known as "totality," will probably start at 2:41 a.m. ET and last 72 minutes.
As for the best time to witness the cosmic event, NASA suggests being outside at 3:17 a.m., "when the moon will be in deepest shadow, displaying the most fantastic shades of coppery red."
Although the arrival of the solstice cannot be seen, the moment describes the instant when the Earth's axial tilt is farthest away from the sun, resulting in the shortest day of the year as well as the longest night of the year.
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- The last time a lunar eclipse fell on the winter solstice was 372 years ago, in 1638, not 456 years ago, in 1554, as reported in a previous version of this story.Dec 20, 2010 1:11 PM ET