January 2007

by Deane Morrison

Like the sash worn by the new year's baby, January sports a diagonal ribbon of its own. The Milky Way stretches across the sky from northwest to southeast, running right through the zenith--the point directly overhead. That bright multicolored star near the zenith is Capella, the jewel of Auriga, the farmer and former charioteer.

To the east, Leo, the lion, raises its kingly head above the horizon. Preceding Leo into the sky, Saturn shines just west of Regulus, the bright star at the lion's heart. Saturn moves a little farther away from Regulus during January, all the while getting nearer to us. Next month we'll have a close encounter with the ringed planet as Earth overtakes it in the race around the sun.

Four planets appear as morning or evening "stars." Venus climbs ever higher in the southwest after sunset, joined by dimmer Mercury late in the month. On the 20th, a thin young moon comes out above the planet; in between them you may be able to pick out two stars in the tail of Capricornus with binoculars. Early birds can see Jupiter low in the east before dawn. Mars, hugging the horizon below Jupiter, will hardly be visible except through a telescope. Also keeping company with Jupiter is Antares, the red heart of Scorpius. On the morning of the 15th, a waning crescent moon makes it a threesome as it hangs like a pearly sickle below Antares.

The full moon of January is known as the wolf moon, old moon or moon after yule. It traces a high arc across the sky the night of the 2nd, becoming full around sunrise on the 3rd and then promptly setting in the northwest.

In the west-northwest, the Great Square of Pegasus is wheeling out of sight. Above and behind the Great Square, the oval form of our neighbor galaxy, Andromeda, still makes a good object for telescopes or binoculars. Andromeda lies between Pegasus and the W- or M-shaped constellation Cassiopeia, the vain queen of Greek mythology. Cassiopeia's boasting of her beauty angered the sea god Neptune and almost led to the sacrifice of her daughter, Andromeda, who was saved from a ravaging sea monster by the hero Perseus.

The constellation Cassiopeia is home to a beautiful, nearly circular remnant of an exploded star called Cassiopeia A. University of Minnesota astronomers recently uncovered some details about the explosion that showed it wasn't, as astronomy professor Lawrence Rudnick puts it, "chaotic enough to stir its remains into one big pile of mush." Understanding how stars explode helps explain how the chemical elements that formed the sun, the Earth and our bodies are created and come together to make new worlds.

The Earth reaches perihelion, the closest point to the sun in its orbit, on the 3rd. The sun will still be a comfortable 91.4 million miles away--not enough for us to feel any effects.

Around the 2nd or 3rd we experience the latest sunrise of the year. By the 21st we'll have about nine hours and 22 minutes of daylight--less than an hour more than the eight hours and 45 minutes on the winter solstice. In contrast, look at what happens to the residents of Fairbanks, Alaska. Their five hours and 45 minutes of daylight on Jan. 21 represents a proportionally huge increase over the three hours and 42 minutes of daylight on the winter solstice.

The reason for the discrepancy is that although the dates of earliest sunset and latest sunrise vary with latitude, the solstices are the shortest and longest days of the year everywhere. In far northern places like Alaska, the day length thus has the same amount of time to switch from shortest to longest and back again as it does at our latitude. But in Alaska it has a lot further to go because the day length at the solstices varies from "midnight sun" to mid-afternoon darkness. Therefore, the day length must change rapidly in Alaska and at other high latitudes.