December is the month of the winter solstice, which a large part of mankind associates with such celebrations as Nativity festivals. The moment of the solstice occurred on Dec. 21 at 5:02 a.m EST (10:02 UT): The sun, appearing to travel along the ecliptic, reached that point in the sky where it is farthest south of the celestial equator.
The Yuletide evening sky is especially rewarding now. The eastern sky is filled with brilliant stars — sort of a celestial Christmas tree. Distinctive groupings of stars forming part of the recognized constellation outlines, or lying within their boundaries, are known as asterisms. Ranging in size from sprawling naked eye figures to minute stellar settings, they are found in every quarter of the sky and at all seasons of the year. The larger asterisms — ones like 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 is in the northwest these frosty evenings.
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, it 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 Cross is best oriented for viewing now, appearing to stand majestically upright on the northwest horizon at around 8:30 p.m. local time, forming an appropriate Christmas symbol. Furthermore, just before dawn on Easter morning the cross lies on its side in the eastern sky.
A 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 make up the decorative bow.
Now you can see how our modern imagination might work, but tradition tells us that those seven stars formed a mighty hunter called Orion, the most brilliant of the 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 seems to us a vague and shadowy figure. The ancient mythological stories of Orion are so many and so confused that it is almost impossible to choose among all of them. Even the origin of the name Orion is obscure, though some scholars have suggested a connection with the Greek “Arion,” meaning simply warrior.
All, however, agree that he 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 and which he is brandishing in the face of Taurus, the Bull, who is charging down upon him.
The heavenly manger
Speaking of Orion’s belt, the legendary French astronomer Nicolas Camille Flammarion (1842-1925) referred to the three belt stars of Orion as “The Three Kings.” And if we were to consider these three stars as representing the Magi, then not too far away, to the east, within the faint zodiacal constellation of Cancer, is the star cluster known as Preasepe, the Manger.
A manger is defined as a trough or open box in which feed for horses or cattle is placed. But the 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, Preasepe represents the manger where Christ was born.
In the sky, 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. It’s completely devoid of any bright stars and would probably not even be considered a constellation at all were 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; Asselus Borealis and Asselus Australis bracket Preasepe to the north and south, respectively. To the unaided eye the manger appears as a soft, fuzzy patch or dim glow. But in good binoculars and low-power telescopes, it 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 Preasepe not as one fuzzy star, but as “a mass of more than 40 small stars.”
The Shepherd’s Star
If you are up about an hour or so before sunrise, look toward the east-southeast to get a glimpse of what Flammarion described as “The Shepherd’s Star,” the planet Venus. He 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 and this year it will remind those who arise early on Christmas morning of the Biblical “Star in the East.”
Lastly, for those who receive a telescope for a holiday gift, while Venus will be rather disappointing, appearing as nothing more than a dazzling dot of light, there are four other splendid planetary targets to gaze at.
On Christmas, the moon will be a waxing gibbous moon four days past first quarter and will be one-quarter up from the eastern horizon by four in the afternoon local time. A couple of hours later the sky will be dark and our nearest neighbor in space will be well placed for observation for those who have just acquired binoculars or a telescope as a holiday gift.
Your best views will be along the line separating day and night on the lunar surface, called the terminator. It is there where craters will appear heavily shadowed and will stand out in sharp relief. The rest of the lunar disk will appear dazzling to the eye. Take note of the crater Tycho near the moon’s lower limb, appearing like a sunflower with brilliant rays emanating from it in all directions. To the left of the moon’s center is another vivid crater, Copernicus.
Then there are the planets. Four days past their “Great Conjunction” are Jupiter and Saturn. Jupiter is that very bright “star” that you notice at day’s end in December, glowing low above the southwest horizon right after sundown; a superb telescopic showpiece with clouds bands crossing its disk, as well as its retinue of four large moons, though tonight only two are visible, Callisto on one side, Ganymede on the other. And just one-half degree – the apparent width of a full moon — to the lower right of Jupiter, is “the lord of the rings,” Saturn. A telescope magnifying 30-power or more will reveal Saturn’s famous rings, now tilted more than 20-degrees to our line of sight.
And finally, as darkness falls, take note of yellow-orange Mars well to the left of the moon, which will continue to fade as it recedes from the Earth. You’ll need a telescope with an eyepiece of at least 160-power to magnify its disk to a reasonable size.
Spot the International Space Station
The largest human-built space vehicle is currently making southwest-to-northeast passes across North America at dawn. To the unaided eye, the ISS appears as a very bright, non-twinkling “star” moving with a steady speed across the sky. To get the latest times and directions to look for it, visit spotthestation.nasa.gov/sightings, which provides sighting information for thousands of locations worldwide.
So, early before sunrise on Christmas morning, why not take your kids outside and wave a holiday greeting to the people on board the station as they fly over your neighborhood at 17,500 miles (28,000 kilometers) per hour?
Joe Rao serves as an instructor and guest lecturer at New York’s Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers’ Almanac and other publications. Follow us on Twitter @Spacedotcom and on Facebook.