January 2006

by Deane Morrison

Look to the setting sun on New Year's Day and you'll see a thin crescent moon poised above the horizon. But you may not see a second, much smaller crescent in the same patch of sky. Venus, now angling closer to us, appears as a long silvery sliver of light, just like the young moon and about nine degrees to the right of it. With binoculars you may be able to discern the shape of Venus if you look just as the sun is setting. After sunset Venus will be engulfed in glare and its crescent shape lost to the eye.

Venus presents this lovely apparition as a sort of last hurrah before dropping like a stone from the sky. Second only to Mercury in orbital speed, Venus disappears into the sun's afterglow during the second week of January and sweeps between Earth and the sun on the 13th. But the disappearance is short-lived. The queen planet re-establishes its throne in the morning sky just a few days later and ends the month rising almost two hours before the sun.

Across the sky to the east, Saturn rises a couple of hours after sunset on the 1st but rapidly shortens the interval. On the 27th, Earth passes directly between Saturn and the sun and the ringed planet rises, gloriously bright, at sunset and shines all night long. During January Saturn moves westward against the backdrop of stars, a path that takes it through the southernmost stars in the Beehive cluster. Saturn and the Beehive make a striking ensemble, especially if you catch them in the same binocular field.

In other planetary news, Mars, still bright but dimming, is high in the south near the Pleiades star cluster after sunset and Jupiter is well up in the southeast at dawn. While Mars is working its way westward and will disappear this summer, the yellow-tinged king of planets is heading out of the morning sky toward a more convenient evening viewing position. By early May Jupiter will be rising around sunset.

The full moon of January was known to many Algonquin Indian tribes as the full wolf moon, for the hungry wolves howling in the numbing cold and snow. Also known as the old moon or moon after yule, it occurs in the wee morning hours of the 14th and traverses the night sky in close company with Pollux, the brighter of the Gemini twins. Fifteen days later, on the 29th, the moon will be new, which means Earth, the sun and the moon will be aligned with the moon in the middle. On the next day the moon reaches perigee, its closest approach to Earth in its monthly cycle. The combination of new moon and perigee makes for powerful tidal forces, so if you're traveling to a coastal area you may witness some especially high tides.

The moon contributes to at least one more celestial spectacle this month. On the morning of the 25th, its waning crescent makes a fetching duo with the red star Antares in Scorpius.

The Quadrantid meteor shower peaks on the 3rd, but the peak is very sharp and occurs around noon Central time. Still, if you look toward the northeast after midnight that night or the previous night, you may see meteors radiating from the northern end of Bootes, the kite-shaped constellation marked by the bright star Arcturus.

Earth reaches perihelion, the closest point to the sun in its orbit, on the 4th. We'll be only 91.4 million miles from our parent star, but of course that's not nearly close enough to feel any warming of winter's chill.

This is the best month to see the winter constellations Orion, Taurus, Auriga, Gemini, Canis Minor and Canis Major. They are particularly beautiful this year, being bracketed by Saturn to the east and Mars to the west. The brightest star in the night sky, Sirius, twinkles at the southern edge of the group. Only 8.6 light-years away, Sirius owes its brightness to its proximity. But in 1862 it was discovered that the star has a small companion that is 10,000 times dimmer, a white dwarf star named Sirius B. White dwarfs are stars like the sun that have used up their nuclear fuel and collapsed to a tiny remnant of their former selves. They have very intense gravity and sometimes explode as supernovas.

Recently, astronomers used the Hubble Space Telescope to study how the gravity of Sirius B stretches light waves from the star to longer, redder wavelengths. From the data they calculated that Sirius B has about 98 percent the mass of the sun but a diameter slightly less than Earth's. Also, the star's gravity is 350,000 times that of our planet, which means a person weighing 125 pounds on Earth would tip the scales at more than 43 million pounds on Sirius B. For more about the study and a picture of the main star and its tiny companion, see http://hubblesite.org/newscenter/newsdesk/archive/releases/2005/36/ .