The Night Sky in February 2012
By Harry J. Augensen
Professor of Physics & Astronomy, Widener University
Full "Snow" Moon on the 7th New Moon on the 21st
Stars and Constellations
Clear, crisp February nights bring with them not only frigid temperatures but also a brilliant tapestry of winter stars. 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, the Hyades. Further to the west of the Hyades is the more compact Pleiades star cluster, looking like a miniature dipper. Following Taurus to the east is Gemini and its two brightest stars Pollux and Castor. 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.
Just below and to the left of Orion is the brightest star in the night sky, Sirius, in the constellation Canis Major.
The four brightest stars in Canis Major form a trapezoidal shape, consisting of Sirius (Alpha), Mirzam (Beta), Adhara (Epsilon), and Wezea (Delta), going clockwise from Sirius. Sirius is by far the brightest of the foursome, with the other three stars having apparent brightnesses roughly comparable with the second magnitude stars in the Big Dipper. But the impression of relative brightnesses was found to be completely misleading, once astronomers determined distances to these objects. Sirius, the Dog Star, is one of the Sun’s nearest neighbors, at only 8.6 light years distance. This distance was first deduced by trigonometric parallax in 1838 by the German astronomer and mathematician Friedrich Bessel. The other three are much farther away: Adhara is 480 light years, Mirzam is 720 light years, and Wezea is 3800 light years distant from our solar system. For any star to lie at these immense distances must imply that it is intrinsically very luminous, far more than our humble Sun. In fact, Sirius possesses a total luminosity 26 times that of the Sun, but the luminosities are 5000, 7200, and 130,000 solar luminosities for Adhara, Mirzam, and Wezea, respectively. Clearly, these are no ordinary stars.
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. 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. The appearance of these groups is a sure celestial sign that spring will soon be here.
Naked-Eye Planets In the Evening and Morning Sky
Mercury reaches superior conjunction with the Sun on the 7th, and is therefore too close to the Sun to be glimpsed for the first half of February. Toward the end of the month, however, Mercury swings up into the evening sky, setting about an hour and a half after the Sun by month’s end. At that time, look for what appears to be a yellow star low above the western horizon about 30 minutes to an hour after sunset.
Venus is like a dazzling yellow gem hovering above the southwestern horizon at dusk. Throughout February, Venus sets about three and a half hours after the Sun, allowing plenty of time to observe it well into the early evening. See how soon you can spot Venus with the unaided eye moderately high in the southwest after sunset.
Jupiter continues to shine brightly high in the south-southwest during the evening hours, resembling a brilliant golden star in the otherwise dim constellation Aries. Jupiter is second only to Venus among the planets in brightness, and it remains in good position for viewing until late evening. As February opens, Jupiter is setting in the west around midnight, over three hours after Venus dips below the horizon. By month's end, Jupiter is setting at about 10:30 pm EST, less than an hour after Venus. With each passing night, Jupiter is sinking closer toward the horizon, while Venus is ascending. The two planets will ultimately cross paths in a spectacular planetary conjunction next month.
Last February, Mars was in conjunction with the Sun and completely unobservable. This February is another story entirely, with Mars approaching its opposition point with the Sun in early March. As February opens, Mars resembles a very bright orange-red star in the constellation Leo. Mars rises at about 8:30 pm at the beginning of February, and a little before 6 pm at the end of the month. By the end of February, Mars will be nearly the same brightness as Sirius, the brightest star in the night sky. Amazingly, light takes only about 6 minutes to reach us from Mars, while it takes 8.7 years to reach us from Sirius! Enjoy the color contrast between the two disparate bodies: Mars glows distinctly orange-red while Sirius shines with a bluish white color.
Rising in the east around 11:30 pm at the start of February, Saturn resembles a bright cream colored star located below Spica, Virgo’s brightest star. By month’s end, Saturn is rising a little after 9:30 pm, around the same time that Venus is setting. Even a modest telescope will reveal Saturn’s magnificent ring system.
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/