The Yuletide evening sky should provide a dazzling sight for anyone willing to brave the cold this season.
The eastern sky is filled with brilliant stars, creating a sort of celestial Christmas tree. This December 2010 sky map depicts a view of some of the constellations visible on Christmas in the Northern Hemisphere.
Distinctive groupings of stars forming parts of recognized constellations, or lying within their boundaries, are known as asterisms. Ranging in size from sprawling naked eye figures to minute stellar arrangements, they are found in every quarter of the sky and at all seasons of the year.?
The larger asterisms ? ones such as the Big Dipper in Ursa Major and the Great Square of Pegasus ? are often better known than their host constellations. One of the most famous asterisms is in the northwest sky these frosty evenings.? [Top 10 Winter Sky Targets]
The Northern Cross
Originally known simply as "the Bird" in ancient times, without any indication of what sort of bird it was supposed to represent, one star grouping later became the constellation Cygnus, the Swan.?
But the brightest six stars of Cygnus compose an asterism more popularly called the Northern Cross.? Bright Deneb decorates the top of the cross. Albereo, at the foot of the cross, is really a pair of stars of beautifully contrasting colors: A third magnitude orange star and its fifth magnitude blue companion are clearly visible in even a low-power telescope.?
While usually regarded as a summertime pattern, the Northern Cross is best oriented for viewing now, appearing to stand majestically upright on the northwest horizon at around 8:30 p.m. local time in the Northern Hemisphere, forming an appropriate Christmas symbol. Furthermore, just before dawn on Easter morning, the cross lies on its side in the eastern sky.
The Christmas package
Look over toward the southeast part of the sky at around the same time. Can you see a large package in the sky, tied with a pretty bow across the middle?? Four bright stars outline the package, while three close together and in a straight line form the decorative bow.?
This is a picture easily put together by our modern imagination, but tradition tells us that those seven stars form a mighty hunter called Orion, the most brilliant of all constellations and visible from every inhabited part of the Earth. Two stars mark his shoulders, two more his knees and three his belt.
As is also the case with the mighty Hercules, the figure of Orion has been associated in virtually all ancient cultures with great national heroes, warriors, or demigods. Yet, in contrast to Hercules, who was credited with a detailed series of exploits, Orion is more of a vague and shadowy figure.?
The ancient mythological stories of Orion are so many and so confused that it is almost impossible to choose between them. Even the origin of the name Orion is obscure, though some scholars have suggested a connection with the Greek "Arion," meaning warrior.?
All, however, agree that Orion was the mightiest hunter in the world, and he is always pictured in the stars with his club upraised in his right hand. Hanging from his upraised left hand is the skin of a great lion he has killed, which he is brandishing in the face of Taurus, the Bull, who is charging down upon him.??
The heavenly manger
The legendary French astronomer Nicolas Camille Flammarion (1842-1925) referred to the three belt stars of Orion as "The Three Kings." And if we assume these three stars represent the Magi, then not too far away, to the east, within the faint zodiacal constellation of Cancer, is the star cluster known as Praesepe, the Manger.?
A manger is defined as a trough or open box in which feed for horses or cattle is placed. But the biblical Book of St. Luke also tells us that the baby Jesus, wrapped in swaddling clothes, was set down in a manger because there was no room at the inn. In our current Christmas week evening sky, Praesepe could represent the manger where Christ was placed.?
The constellation of Cancer is practically an empty space in the sky, positioned between the twin stars Pollux and Castor of Gemini and the Sickle of Leo. Cancer is completely devoid of any bright stars and would probably not be considered a constellation at all were it not for the fact that there had to be a sign of the zodiac between Gemini and Leo.
In the middle of Cancer are two stars called the Aselli ("Donkeys") that are feeding from the Manger; Asellus Borealis and Asellus Australis bracket Praesepe to the north and south, respectively. To the unaided eye, the Manger appears as a soft, fuzzy patch or dim glow.
But using good binoculars and low-power telescopes, the Manger is a beautiful object to behold, appearing to contain a splattering of several dozen stars. Using his crude telescope, Galileo wrote in 1610 of seeing Praesepe not as one fuzzy star, but as "a mass of more than 40 small stars."
The shepherd's star
If you are up before sunrise, toward the east-southeast to get a glimpse of what Flammarion described as "the shepherd's star," also known as the planet Venus. Flammarion wrote:
"She shines in the east in the morning, with a splendid brightness which eclipses that of all the stars. She is, without comparison, the most magnificent star of our sky; the star of sweet confidences."
Indeed, Venus is always bright, but this December its brilliance and altitude are exceptional. This month, from mid-northern latitudes, the lamp-like "Morning Star" rises nearly four hours before sunrise. It may remind those who arise early on Christmas morning of the biblical "Star in the East."
Your clenched fist held at arm's length measures roughly 10 degrees of the sky. At sunrise Venus will reach a maximum altitude about 32 degrees (more than three fists up from the east-southeast horizon) by Christmas.
On clear mornings you should have little trouble following Venus with the naked-eye until sunrise. And on New Year's Eve morning (Dec. 31), a slender crescent moon forms an eye-catching tableau with Venus in the morning sky. Venus will hover well above and to the left of the moon.
For those who receive a telescope for a holiday gift, Venus will present a dazzling and wide crescent image. But there are also two other splendid planetary targets to gaze at.
That very bright "star" that you notice at day's end in December, glowing high in the south, is Jupiter. The planet offers a superb telescopic showpiece with cloud bands crossing its disk, as well as its retinue of four large moons. By the end of December, it's setting just before 11 p.m. local time.
And lastly, in the predawn morning sky with Venus, is Saturn. On the morning of Dec. 28, the moon will be passing well to the right of both Saturn and the bright star Spica. A telescope magnifying 30-power or more will reveal Saturn's famous rings, now tilted 10-degrees to our line of sight.
And of course, don't forget to look for one of the most exciting celestial events of the year, when the moon is in total eclipse Monday night (Dec. 20). [Total Lunar Eclipse Viewer's Guide]
- Top 10 Winter Sky Targets
- Telescopes for Beginners
- 10 Hubble Space Telescope Targets You Can Find Too
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.