January 2008

by Deane Morrison

The weather may be cold, but January is a hot month this year for spotting celestial objects that have made news. First is none other than Mercury, the elusive messenger of the gods.

Mercury pops into the evening sky in the second week of January, reaching its highest point over the western horizon around the 21st. It appears low in the southwest, to the right of the bright star Fomalhaut. The planet never lingers long, however, and this time it will fade by the end of the month.

This small planet orbits closest to the sun, but despite its relative proximity to Earth we know very little about it. To remedy that, NASA has sent its MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft to study Mercury, and it will make its first flyby on the 14th. The mission seeks to answer several burning questions about the planet, such as how come it's so dense and why both Mercury and Earth have global, internal magnetic fields but the neighboring planets Venus and Mars do not.

A second news-making object lies west of Orion, in the constellation Cetus. It is Mira, a star whose Latin name means "wonderful." Astronomers have recently discovered a tail of gas left by Mira as it hurtles through space. A whopping 13 light-years long, the tail stretches far enough to accommodate several thousand solar systems lined up end to end. The tail, which is visible in ultraviolet light, contains elements that could seed a new generation of stars and planets--maybe even life. Mira can be found by looking below and a little left of the first-quarter moon on the 15th.

January is a good month to see the dim constellation Eridanus, which University of Minnesota astronomers put in the news a couple of months ago. Tracing a meandering course from near Rigel, in Orion, down to the southern horizon, the river Eridanus marks the location of a gigantic void in the Universe that was discovered by U of M astronomy professor Lawrence Rudnick, associate professor Liliya Williams, and graduate student Shea Brown.

The void can't be seen with the human eye because it's between six billion and 10 billion light-years distant, and the stars of our Milky Way galaxy fill the visible sky in front of it. But if you could see it, it would be huge. Close to a billion light-years across, it covers an area of the sky about three degrees in diameter, approximately 40 times the area covered by the full moon. Its presence gives astrophysicists the task of explaining why the distribution of matter in the Universe isn't as even as had been thought.

Mars, still very bright but fading, forsakes Gemini for Taurus this month. It still makes a worthy ornament for its celestial neighborhood, which includes Sirius, the brightest of stars. Saturn, trailing Mars in the spring constellation Leo, rises ever earlier in the evening and will appear in full glory late in February.

Turning to the morning sky, Venus and Jupiter approach each other all month long just above the eastern predawn horizon. The two planets move relative to each other at a pretty good clip because Venus, the brighter, is dropping as it prepares to swing behind the sun while Jupiter is climbing. On February 1 the two beacons will pass each other.

The full moon of January, called the old moon or wolf moon by Algonquin Indian tribes, arrives at 7:35 a.m. on the 22nd, just a few minutes before sunrise and less than half an hour before the moon sets in the northwest.

Earth reaches perihelion, its closest point to the sun, on the 2nd. At that moment we'll be about 91.4 million miles from our parent star--not close enough to feel any extra warmth.