The Night Sky: February 2010

Contents

The Night Sky in February 2010

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

Moon’s Phases
New Moon on the 13thFull "Snow Moon" on the 28th                            

Stars and Constellations

February skies present a brilliant tapestry of stars that contrasts with the frigid temperatures of winter nights.  The constellation Cassiopeia, which represents the throne of the Queen of ancient Ethiopia, can be seen high in the northwest, looking like the letter "M."  Even higher in the northwest above Cassiopeia is Perseus, whose brightest stars form a “horn” shape which opens toward the nearby Pleiades cluster.   Nearly overhead on February evenings is Auriga, the Charioteer, with the bright yellow star Capella as its "eye." Just south of Auriga is Taurus the Bull, with its bright orange star Aldebaran.  Aldebaran is classed as a red giant star, and it stands in the foreground of a more distant loose cluster of stars known as the Hyades.  Further to the west of the Hyades is the more famous and compact Pleiades star cluster, looking like a miniature dipper. 

Following Taurus to the east is Gemini, the Twins, and its two brightest stars Pollux and Castor.  Their proximity to each other is merely perspective:  in reality they are about 10 light years apart.  Pollux has a slight yellow or orange tinge to it, while Castor is more white in color.  Remarkably, the Castor system consists of a total of six gravitationally bound stars, five of which can be seen individually in a telescope.  In ancient mythology, Pollux and Castor were the offspring of the god Zeus and the mortal Queen of Sparta. Pollux was born immortal, but Castor was mortal.  Both brothers were among the crew of Jason and the Argonauts.  Gemini is a significant zodiac constellation because it contains the summer solstice point, which the Sun passes through on or about June 21, the first day of summer.  In fact, the Sun’s apparent path around the celestial sphere (defined as the ecliptic) takes it within the boundaries of Gemini during the time interval from June 20 through July 20.

Orion the Hunter now stands high in the south, dominating the midwinter night sky.  Orion's two brightest stars, Betelgeuse and Rigel, are classed, respectively, as red and blue supergiants, and are among the most luminous stars known.  Orion's "sword" contains the Great Orion Nebula, a vast complex of star formation nearly 1500 light years from our solar system.  Just below and to the left of Orion is the brightest star in the night sky, Sirius, in the constellation Canis Major.  Sirius is one of the Sun’s nearest neighbors, at only 8.5 light years distance.  Sirius is actually a binary star system, consisting of a bright primary star with a very faint companion. The companion is now known to be a white dwarf, or degenerate star, in which nuclear reactions are no longer sustained, and possessing a diameter of only 1/100 that of the Sun, or nearly the same size as planet Earth. Just a bit further to the east of Sirius is its neighbor Procyon in Canis Minor.  Like Sirius, Procyon is also nearby, at 11 light years away, and also like Sirius, Procyon is a binary star system containing a white dwarf.  Betelgeuse, Sirius, and Procyon comprise a "winter triangle." Though not nearly as famous as its summer counterpart, the winter triangle is nevertheless easy to pick out since the stars are bright.

After about 8 pm, you can spot some of the stars of spring mounting the sky in the east.  In particular, Regulus in the constellation Leo, lies low in the east-northeast.  Looking a little further northward, you may spot the Big Dipper, which is part of the constellation Ursa Major, or Big Bear, rising in the north-northeast.  Seasoned skywatchers know that when they see these celestial signs spring is is just around the corner!

 Naked-Eye Planets In the Evening and Morning Sky 

Venus was in conjunction with the Sun last month, and is still too close to the Sun to be visible at the beginning of February.  Toward the middle of the month, however, Venus begins to emerge from the evening twilight.  At midmonth, Venus passes very close to Jupiter, which is sinking toward the Sun.  By month’s end, Venus sets nearly an hour after sunset and, for those with an unobstructed horizon, can be seen shining low above the western horizon.

  The Giant Planet, Jupiter, can still be spotted very low in the southwestern sky after sunset in early February, but not for long ;  it  will vanish into the evening twilight before the end of the month.  Jupiter, which resembles a brilliant cream-colored star hovering above the southwestern horizon after darkness falls, has dominated the evening sky since last summer, but this month it yields the celestial stage to Mars .  At the beginning of February, Jupiter sets at 7 pm, or only about an hour and a half after sunset.  On the 16^th, descending Jupiter passes only a Full Moon’s width fromVenus, which is moving the opposite way.  On the last day of February, Jupiter will be in conjunction with the Sun and unobservable.  

As Jupiter sets into the western twilight, the Red Planet, Mars, rises in the eastern sky.  Mars, which was closest to Earth and at opposition with the Sun at the end of January, now reigns supreme among planets in the night sky.  Mars resembles a bright orange star in the northeast during the early evening hours, but it gets higher as the night progresses, and stays in good view until shortly before sunrise.  Even a small telescope should reveal some of the surface markings and polar caps.  At the beginning of the month, Mars is about as bright as Sirius, the brightest star in the night sky, which can be located just below and to the left of Orion.  As Earth pulls away from Mars over the next few weeks, Mars will begin to dim in brightness, and by month’s end, Mars will have faded to about half the brightness it had when at opposition. 

Saturn, now in eastern Virgo, rises by 9:30 pm at the beginning of February, and looks like a bright yellow star rising above the eastern horizon in late evening.  Saturn’s yellow color contrasts with the blue-white sparkle ofVirgo’s brightest star, Spica which lies to Saturn’s lower left.  By month’s end, Saturn sets around 7:30 pm, and next month will be in opposition with the Sun.   Saturn is not as bright as Mars, but its fabulous ring system is worth a look through a telescope.

Mercury, which reached greatest morning elongation with the Sun on January 27^th, is still in good position for morning viewing as February opens.  To spot Mercury, look for what appears to be a bright yellow star low in the south east a half-hour to an hour before sunrise.  As February progresses, however, Mercury will sink into the morning twilight and be unobservable by month's end. 

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.