The Night Sky: January 2009

Contents

The Night Sky in January 2009

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

Moon’s Phases in Month
  Full "Wolf" Moon on the 11thNew Moon on the 26th

Stars and Constellations

The clear, cold nights in January offer great rewards for braving the frigid conditions.  A few autumn stars are still visible, including those belonging to Cetus, the Whale, and the four stars which comprise the Great Square of Pegasus, which are now setting in the west.  But the rest of the evening is ruled by the brilliant 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, whose eye is the bright yellow star Capella.  The name Capella is derived from Latin, and means “little she-goat,” a likely reference to the mythological goat that suckled the baby Zeus.  Capella is 42 light years away from our solar system and, although it appears as a single object to the eye, astronomers have deduced that it really consists of two stars, each of which is a giant over 10 times bigger in diameter than our Sun.  Just south of Auriga is Taurus the Bull, a zodiac constellation.  Taurus contains not only the bright orange star Aldebaran but also the compact star cluster  the Pleiades, or the Seven Sisters.  Just east of Taurus is another zodiac group, Gemini, which contains the “twin” stars Pollux and Castor.

By far the most brilliant of all the winter constellations is Orion, the Hunter, which stands high in the south around the midnight hour during January. Orion is a veritable jewel box of relatively young stars, most of which lie hundreds or even thousands of light years from our solar system.  These include the four stars which outline his major perimeter (listed clockwise from the upper left):  Betelgeuse (pronounced beetle-juice), Bellatrix, Rigel, and Saiph. Betelgeuse is a red supergiant, similar to the summer sky's Antares in Scorpius.  The other three are blue supergiants or giants.  Cutting across Orion’s middle is his belt, a very distinct line of three bluish-white stars, Alnitak, Alnilam, and Mintaka.  Alnitak and Alnilam lie over 1000 light years from our solar system and Mintaka is over 2000 light years distant. Extending downward from Orion’s belt is his sword, which contains the Orion Nebula, officially designated as Messier 42, a birthblace for thousands of new stars.  It lies at a distance of 1500 light years.

Two faithful dogs, Canis Major, the Big Dog, and Canis Minor, the Little Dog , are found to Orion’s upper and lower left, respectively.  Canis Major contains the brightest appearing star in the sky, Sirius, which looks like a brilliant bluish-white beacon in the southeast during the evening hours of early winter. Canis Minor has his own bright star, Procyon, the “Pup.”  Sirius and Procyon are among the Sun’s nearest 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 was such a glorious sight in the evening sky last summer, can still be spotted low above the southwestern horizon after sunset, but not for long.  After about the first week of January, it vanishes into the twilight.  Before it bids (temporary) farewell to the evening sky, Jupiter pairs up with Mercury on New Year’s Day, when the two planets pass close to each other in the sky.  Jupiter reaches conjunction with the Sun on the 24^th, and will slowly reappear in the morning sky during February.  Mercury begins January in close proximity to brighter Jupiter, low in the southwestern sky at dusk, so you will need to have a clear view of the horizon to see them.  Mercury reaches its greatest evening elongation with the Sun on the 4^th, but thereafter it descends rapidly toward the Sun. Mercury passes between the Earth and Sun (inferior conjunction) on the 20^th, after which it moves into the dawn sky.

Among the planets visible this month, Venus takes pride of place, blazing like a brilliant yellow star in the southwest during the early evening hours. Venus reaches its greatest evening elongation with the Sun on the 14^th, and sets nearly 4 hours after sunset all month (around 9 pm for much of the continental US), giving observers plenty of time to see it.  A telescope reveals that Venus is half-illuminated, or at “quarter phase.”  Around the 22^nd, Venus passes close (apparently) to the faint planet Uranus, making for an interesting sight in binoculars or a small telescope.

Saturn, which now lies in the constellation Leo on the border with Virgo, appears in late evening, rising around 10:30 pm EST on New Year’s Day and by 8:30 pm at month’s end.   Once it is well up, Saturn is easily located, resembling a bright yellow star high in the east-southeast, roughly halfway between first-magnitude stars Regulus and Spica.  Saturn’s system of rings is currently tilted nearly on edge, and so it will not be very prominent in a telescope.

Mars, which was in conjunction with the Sun last month, is still too close to the Sun to be viewed, but should begin to reappear faintly in the pre-dawn sky by the end of February.  Mars will eventually work its way back to the evening sky in late 2009, and by January 2010, one year from now, Mars will return to glorious form when it makes its closest approach to Earth since December 2007. 

Earth reaches perihelion, or closest approach to the Sun, on January 3, when it will be about 3.5% closer to the Sun than it was in July.  Note that it is not this effect, which results directly from the eccentricity of Earth’s orbit, but rather the tilt of Earth’s axis, which causes seasonal variations.

The Quadrantid meteor shower should peak on or around January 3.  The meteors appear as Earth speeds through the debris trail left behind by an object known as 2003 EH1, probably a comet fragment. The particles burn up as they enter Earth’s atmosphere, creating luminous streaks. 

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