As a lunar eclipse coincides with winter solstice, stargazers can watch the moon turn pink, perhaps even red.
A lunar eclipse is expected in the early morning hours of Tuesday.
The eclipse coincides with the mid-winter solstice.
The event will make the moon appear pink or red.
Weather permitting, skygazers in northern America and Europe are in for a treat in the early morning hours of Tuesday, when the first total lunar eclipse in almost three years is poised to turn the moon pink, coppery or even a blood red.
Coinciding eerily with the northern hemisphere's mid-winter solstice, the eclipse will happen because the sun, the Earth and its satellite are directly aligned, and the moon swings into the cone of shadow cast by its mother planet.
The moon does not become invisible, though, as there is still residual light that is deflected towards it by our atmosphere.
Most of this refracted light is in the red part of the spectrum and as a result the moon, seen from Earth, turns a reddish, coppery or orange hue, sometimes even brownish.
"The entire event is visible from North America, Greenland and Iceland," says NASA's veteran eclipse expert Fred Espenak, pointing out that for observers in the western United States and Canada, the show will start on Monday evening rather than Tuesday morning.
"Western Europe will see the beginning stages of the eclipse before moonset, while western Asia will get the later stages after moonrise."
The eclipse runs for three and a half hours, from 6:33 GMT to 10:01 GMT (1:33 a.m. EST to 5:01 a.m. EST), although the stage of total eclipse -- when the moon heads into the "umbra" cast by the Earth -- lasts from 7:41 to 8:53 GMT (2:41 a.m. EST to 3:53 a.m. EST).
Two factors affect an eclipse's color and brightness, says the astronomy magazine Sky & Telescope.
"The first is simply how deeply the moon goes into the umbra. The center of the umbra is much darker than its edges," it says.
"The other factor is the state of Earth's atmosphere along the sunrise-sunset line. If the air is very clear, the eclipse is bright. But if a major volcanic eruption has polluted the stratosphere with thin haze, the eclipse will be dark red, ashen gray, or blood-black."
Lunar eclipses have long been associated with superstitions and signs of ill omen, especially in battle.
The defeat of the Persian king Darius III by Alexander the Great in the Battle of Gaugamela in 331 B.C. was foretold by soothsayers when the moon turned blood-red a few days earlier.
And an eclipse is credited with saving the life of Christopher Columbus and his crew when they were stranded without supplies on the coast of Jamaica.
According to legend, Columbus, looking at an astronomical almanac compiled by a German mathematician, realized that a total eclipse of the moon would occur on Feb. 29, 1504.
He called the native leaders and warned them if they did not help, he would make the moon disappear the following night.
The warning, of course, came true, prompting the terrified people to beg Columbus to restore the moon -- which he did, in return for as much food as his men needed. He and the crew were rescued on June 29, 1504.
The last total lunar eclipse took place on Feb. 21, 2008. Next year, says Espenak, will see two: on June 15 and Dec. 10.
A solar eclipse happens when the moon swings between the Earth and the sun.