Three nights before Christmas, clear skies around the world will shine with a light not seen in 133 years.
The occasion is the full moon happening Wednesday on the winter solstice just as the moon is tugged closest to both Earth and sun. The result will be a moon that looks bigger and brighter than usual -- not quite a miracle, but nonetheless a rare heavenly event."You should be able to read by the light of the moon if it isn't cloudy," said Bob Strom, a scientist at the Lunar and Planetary Institute in Tucson, Ariz. "So you'll love it."
Judging from the breathless e-mails circulating on the Internet, people already are loving at least the prospect of it.
At least one message that urges people to take a hike or paddle in the moonshine, composed by an unidentified writer, has been forwarded between countless people by e-mail. Glen Erickson, a professor emeritus of physics and adviser to the Astronomy Club at the University of California, Davis, received two different messages. He tried to track the origin of one, but the attempt was futile.
"That's why I tend to be cynical about the Web, it's a lousy source of reliable information," he said.
But when Erickson set out to independently verify the message's claims, he found most of them valid. Richard Marasso, chair of the astronomy department at Sierra College, and Homer Ibser, professor emeritus of astronomy at California State University, Sacramento, likewise confirmed that something is different about the full moon.
Several things are coinciding to make it special:
-- The moon reaches its largest, brightest point every 29.5 days, but this month's peak happens to fall on the winter solstice -- the longest night of the year in the northern hemisphere. Winter solstice full moons happen once every 19 years, by Erickson's reckoning.
-- On the same day, the moon swings closest to the Earth in its slightly elliptical orbit. This point, called perigee, happens every 27 to 28 days, and therefore does not always coincide with the full moon. The frequency of the full moon coming on the same day as solstice and perigee is once every 133 years, Erickson figured.
-- The Earth, also moving in an elliptical orbit, is nearing its closest approach to the sun, known as perihelion. In the northern hemisphere, the Earth is closest to the sun in the winter, farthest in the summer. It is the tilt of the Earth toward and away from the sun, not proximity, that governs the seasons. Because the Earth is close to the sun, and the moon is close to the Earth, that means the moon also is exceptionally close to the sun, making it appear more luminous than usual.
Ibser's calculations show the moon will be 12 percent brighter than usual. Of course, the perception of brightness depends on local conditions. Will it be cloudy or clear? The sky dark or hazy with city lights?
"This is not going to be a real stunner where you have to wear sunglasses. You might look at it and say, this is no big deal," acknowledged Strom, the Lunar and Planetary Institute scientist. "But it is."
Dist. by Scripps Howard News Service