The Night Sky: January 2010

Contents

The Night Sky in January 2010

By Harry J. Augensen
Professor of Physics & Astronomy, Widener University

Moon’s Phases
New Moon on the 15thFull "Wolf Moon" on the 30th                            

Stars and Constellations

Frosty January evenings provide a chance to become acquainted with the brilliant stars and constellations of winter, which are now in their full splendor.  At the beginning of the month, though, you can catch a last look at the Summer Triangle stars  Vega, Altair, and Deneb before they vanish below the northwestern horizon during the early evening.  The remaining representatives of the autumn sky, including the Great Square of Pegasus and the "water" constellations of Pisces (the Fishes) and Cetus (the Whale), will also be setting in the west later in the evening.  The rest of the night belongs to the stars of winter. The constellation Perseus is nearly overhead by 8 pm, just to the east of the upside-down "W" of Cassiopeia.  To the east of Perseus is Auriga, the Charioteer, one of the brightest of winter constellations.  Auriga represents the Greek mythological character Erichthonius, a lame man who invented the horse-drawn chariot so he could travel about.  His "eye" is the bright star Capella, which means "little she-goat."  Capella is the sixth brightest star in the sky, and is actually two stars very close together.

Just south of Auriga is Taurus, the Bull, which contains the bright orange giant star Aldebaran. Aldebaran is a red giant star 25 times larger than or Sun.  By coincidence, Aldebaran is situated in the foreground of the Hyades star cluster;  the two are unrelated, as Aldebaran lies at a distance of 65 light years from our solar system, while the Hyades group is over twice as far away.  Taurus also contains the beautiful and compact star cluster the Pleiades, or Seven Sisters, which lies 440 light years away.  Taurus is an ancient constellation, which in Greek mythology represents the Minotaur, a half-man, half-bull monster.  Another Greek legend states that the Taurus represents the disguise which Zeus assumed in order to seduce the Phoenician king’s daughter, Europa.  Yet another story equates Taurus with the Cretan bull tamed by Hercules as one of his twelve labors.

Just east of Taurus is Gemini, which contains the stars Pollux and Castor.  The most famous of all the winter constellations is Orion, the Hunter, which stands high in the south around the midnight hour during January.  All of Orion’s stars, including his two brightest, orange Betelgeuse and bluish Rigel, are hundreds of light years distant from our solar system.  Orion is accompanied on the hunt by his two faithful dogs, Canis Major, the Big Dog, and Canis Minor, the Little Dog , to Orion’s upper and lower left, respectively.  To Canis Major belongs the brightest star in the night sky, Sirius, the "Dog Star," which looks like a brilliant bluish-white beacon in the southeast during the evening hours of early winter.  Look for Sirius as it rises at 7 pm at the beginning of January, but two hours earlier, or around sunset, by month's end.  Canis Minor has his own bright star, Procyon, the "Pup."  In contrast to the remote stars of Orion, both Sirius and Procyon are among the Sun’s closest neighbors in space, lying at distances of only 8 and 11 light years, respectively. 

 Naked-Eye Planets In the Evening and Morning Sky 

Jupiter, which resembles a brilliant cream-colored star low in the southwest after darkness falls, has been a faithful beacon in the evening sky since last summer. Although still an impressive sight this January, Jupiter's duration in the night sky lessens as it continues to sink toward the southwestern horizon during the course of the month. On New Year’s Day, Jupiter sets by 8:30 pm, but by the 31st, it sets at 7 pm, or only about an hour and a half after sunset. By the end of February, Jupiter will be in conjunction with the Sun and unobservable.

Mars is at its best at the end of January, when it reaches opposition with the Sun and is closest to Earth. (The last time Mars was so favorably positioned was back in December 2007.) Early in the month, Mars rises at 7:30 pm, or about two and a half hours after sunset. By the end of the month, when opposition occurs, Mars rises as the Sun sets, shortly after 5 pm, remains in view all night long, and sets as the Sun rises. Mars resembles a bright orange star low in the northeast during the early evening hours, and gets higher as the night progresses, eventually transiting the meridian high in the south at midnight. A modest telescope should reveal some of the surface markings and polar caps. It is worth noting that Mars will have about the same brightness as the brightest star in the night sky, Sirius, which can easily be located below and to the left of Orion. The color contrast between orange Mars and blue-white Sirius is striking.

Of special note is the fact that during December Mars moved eastward from Cancer into Leo, following typical west-to-east orbital behavior, but this month it shifts westward back into Cancer. This phenomenon mystified ancient astronomers, including many of the Greeks, but today it is easily explained as a result of the Earth, as it orbits the Sun, overtaking and "passing" the more slowly traveling Mars in its outer orbit, thus giving the appearance of backwards motion.

Saturn, currently located among the stars of the constellation Virgo, becomes firmly established as an evening planet this month, rising around 11:30 pm at the beginning of the month and by 9:30 pm at month’s end. Look toward the east at least an hour or so after these times to find yellow Saturn with the blue-white star Spica not far below it. While not nearly as bright as Mars, Saturn is nevertheless worth finding; a telescope or even good binoculars will reveal the famous ring system.

Mercury is in conjunction with the Sun on the 4th, and therefore is not viewable during the first week or so of January. Shortly after conjunction, however, Mercury jumps into the early morning sky, rising nearly one and a half hours before the Sun for the second half of the month. It reaches greatest elongation with the Sun on the 27th. To spot Mercury, look for what appears to be a bright yellow star low in the south east about an hour before sunrise. The other inner planet, Venus, is in conjunction with the Sun on the 11th, and remains lost in the glare of the Sun until the end of February, when it will begin to appear in the evening sky.

Earth reaches perihelion, or closest approach to the Sun, on January 2, when it will be about 3.5% closer to the Sun than it was in July. Note that it is the tilt of Earth's axis, not its orbital eccentricity, which causes the seasons.

For more information on astronomy and weather, visit the Widener University Public Viewing Website at http://www.widener.edu/stargazing/, then click on Web Links & Resources. A set of free sky maps can be obtained at http://www.skymaps.com/

Some content for this article has been obtained from US Naval Observatory Data Services

Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.