The Night Sky: January 2012

December 29, 2011, 8:27 pm
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The Night Sky in January 2012

By Harry J. Augensen

Professor of Physics & Astronomy, Widener University

 

Moon’s Phases
            Full "Wolf" Moon on the 9th                          New Moon on the 23rd

Stars and Constellations

As January begins, only a handful of autumn stars are still viewable, including those belonging to Cetus, the Whale, and the four stars which comprise the Great Square of Pegasus, which are now descending in the west.  The rest of the evening is ruled by the brilliant stars of winter, which offer abundant rewards for braving the frigid conditions.  By 8 pm, the constellation Perseus stands nearly overhead, 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 the 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 several attractions, including the bright orange star Aldebaran, the "V" shaped Hyades star cluster (which Aldebaran happens to lie in front of), and the compact star cluster the Pleiades, or the Seven Sisters.  Just below and to the left of Taurus is unquestionably the most brilliant of all the winter constellations:  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, while the other three are blue supergiants or giants.

Betelgeuse is highlighted in University of Illinois astronomer James Kaler's book, The Hundred Greatest Stars (New York: Copernicus Books, 2002).  The most recent distance measurement using the Hipparchos satellite puts Betelgeuse at roughly 650 light years from our solar system, with a rather large uncertainty of about 150 light years.  Betelgeuse is enormous, with a fuzzy diameter of around 800 solar diameters.  This makes it one of the largest stars known, its diameter having first been measured in 1920 by physicist A. Michelson.  Betelguese is also a very massive star, with about 15 times the mass of the Sun.  Betelgeuse is quite similar in size, temperature, and mass to another famous red supergiant, Antares in Scorpius, which lies in the opposite part of the sky.  Both stars are destined to eventually end their lives violently in brilliant supernova explosions.

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 birthplace for thousands of new stars.  It lies at a distance of 1500 light years.   

Just east of Taurus is another zodiac group, Gemini, which contains the stars Pollux and Castor. 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

Venus is truly magnificent this January, resembling a blazing yellow star above the southwestern horizon at dusk.   On New Year’s Day, Venus sets about two and a half hours after the Sun, and by month's end that interval stretches to over three hours.  It gets dark enough to spot Venus with the unaided eye in the southwest about 20 minutes after sunset.   Those unfamiliar with the night sky may mistake Venus for an airplane landing light, or even a UFO!

As darkness falls in the evening, Jupiter can be spotted high in the south, resembling a brilliant golden star.   Though not as bright as Venus, Jupiter is still a beautiful sight, and it remains visible until long after Venus has set.  Jupiter sets in the west a little before 2 am EST on the 1st, and by midnight on the 31st.

Mars kept a pretty low profile during 2011, but the distance between Mars and Earth is now rapidly shrinking, resulting in Mars doubling in brightness during January.   As January opens, Mars resembles a bright orange star in the eastern part of the constellation Leo, near the border with Virgo.  Mars drifts eastward, and at midmonth it crosses into Virgo, but then by month's end it reverses course and begins to drift back toward Leo.  Mars rises a little past 10 pm on New Year’s Day, and at about 8:30 pm on the 31st. By the end of January, Mars will be brighter than any other visible star except Sirius, the brightest star in the night sky.  And by early March, when Mars reaches opposition with the Sun and is closest to Earth, Mars and Sirius will be nearly equal in brightness, though contrasting greatly in color:  a ruddy red Mars compared with a bluish white Sirius.

Saturn resembles a bright cream colored star located near Spica, the brightest star in Virgo. On New Year’s Eve Saturn rises around 2am, and by month’s end, Saturn is up around 12:30 am.   

Mercury reached its maximum morning elongation with the Sun in late December, and it remains in good position for viewing in the predawn sky during the first week of January.  On the first morning of 2012, Mercury rises about an hour and a half before the Sun.  Look for what appears to be a bright yellow star low above the eastern horizon about 30 minutes to an hour before sunrise.  By midmonth, Mercury is rising only an hour before sunrise, and thereafter it vanishes into the morning twilight, to reappear as an evening “star” in late February. 

Earth reaches perihelion, or closest approach to the Sun, on January 4th, when it will be about 3.5% closer to the Sun than it was in July.  However, it is the tilt of Earth’s axis, not its orbital eccentricity, which causes the seasons.

The peak of the Quadrantid Meteor Shower is predicted to occur in the early morning hours of January 4th.  The origin of this shower is debris left behind by object 2003 EH1, probably a comet fragment.  Look generally toward the east in the hours after midnight, after the bright waxing gibbous Moon has set and no longer interferes with seeing the fainter meteors.

 

Information on lunar phases and rise/set times of Sun and planets is obtained from the US Naval Observatory Data Services at http://www.usno.navy.mil/astronomy/. Additional information comes from Astronomical Calendar 2012 by Guy Ottewell (Raynham, MA: Universal Workshop, 2012)Times given apply for observers near to the latitude and longitude of Philadelphia, USA: 40 degrees North latitude, 75 degrees West longitude.

For more information on astronomy and weather, visit 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/

Glossary

Citation

Augensen, H. (2011). The Night Sky: January 2012. Retrieved from http://www.cosmosportal.org/view/blog/172221

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