The Night Sky: March 2009

Contents

The Night Sky in March 2009

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

Moon’s Phases in Month
  Full "Worm" Moon on the 10thNew Moon on the 26th

Stars and Constellations

The month of March marks the transition between the cold, biting nights of winter and the cool, more tolerable nights of early spring. March is also the month during which the brilliant constellations of winter evenings are gradually replaced by the more modest spring groups.  During the early evening hours, the winter star Aldebaran in Taurus and the nearby Pleiades star cluster are still on display high in the southwest. Just west of overhead is the yellow star Capella, and Betelgeuse and Rigel in Orion are high in the south.  The twin stars Pollux and Castor in the constellation Gemini are high in the east-southeast, while the brightest appearing star in the night sky, Sirius in Canis Major (Big Dog), shines with bluish-white radiance to Orion’s lower left.  The name Sirius means "scorching." The ancient Greeks believed that Sirius was responsible for the heat of summer, since in July and August it appeared in the dawn sky just before sunrise.  The hot, muggy days therefore became known as "Dog Days." 

Sirius is one of the Sun’s nearest neighbors, at only 8.5 light years distance.  Sirius is famous not just because it is the brightest appearing star in the sky, but because it is actually a binary star system, consisting of two components: A and B.  Sirius A has about twice the diameter of our Sun, but Sirius B is a pigmy by comparison.  Having a diameter of only 1/100th that of the Sun, or nearly the same size as Earth, Sirius B is classed by astronomers as a white dwarf, or degenerate star, since it is no longer is sustained by nuclear reactions.  Above and to the left of Sirius is Procyon in Canis Minor (Little Dog).  Procyon is also relatively nearby, only 11 light years away, and it, too, possesses a faint, white dwarf companion star.

As evening progresses into night, the stars of spring begin to emerge from the eastern horizon.  Regulus, the brightest star in Leo (Lion), which stands high in the east, is one of the first spring stars to become visible after dark. Regulus lies about 78 light years from our solar system, and its name denotes "King" or "Royal." Some cultures have even associated Regulus with the birth of Christ.  But the brightest star in the spring sky is yellow-orange Arcturus in the constellation Boötes (the Herdsman), which can now be glimpsed low in the northeast.  Arcturus is the 4th brightest star in the night sky, after Sirius, Canopus, and alpha Centauri (Rigel Kentaurus), but the last two of these are too far south to be seen from most of the continental U.S.  Arcturus is highlighted by University of Illinois astronomer Dr. James Kaler in his book, The Hundred Greatest Stars (New York: Copernicus Books, 2002), stating that Arcturus is an orange giant star with a diameter about 25 times that of the Sun and lying 37 light years from our solar system. The Big Dipper, which is part of the constellation Ursa Major (Great Bear), is also rising in the northeast, and its handle "arcs" to Arcturus.  Arcturus’s name derives from "arktos," the Greek word for "bear." This is appropriate since Arcturus follows Ursa Major around the North Celestial Pole. 

 Naked-Eye Planets In the Evening and Morning Sky

Brilliant Venus has become a familiar sight in the southwestern sky during the early evening  hours this winter, but that is about to change.  Venus begins the month of March in inimitable and spectacular form, blazing like a beacon in the southwest for several hours after sunset.   Even a small telescope reveals that Venus possesses a thin crescent shape, similar to the Moon.  Venus sets a generous 3 hours after the Sun at the beginning of March, giving sky watchers plenty of time to take in its magnificence.  As the month progresses, however, Venus rapidly descends into the evening twilight, and by the 27th Venus reaches inferior conjunction with the Sun, meaning that it is aligned between Earth and the Sun.  Venus reappears in the morning sky at the end of the month, and will remain there for the duration of 2009.

 Saturn reaches opposition with the Sun on the 8th, and hence is in optimal position for viewing:  it rises when the Sun sets, and remains above the horizon all night long.  Saturn cannot compete with Venus in terms of visual brightness, but in a telescope the view of Saturn’s rings is hard to match.  Right now, the ring system is tilted nearly on edge, and so it is not as impressive as is usually the case, but nevertheless the rings are a beautiful sight.  Saturn is easy to spot in the east-southeast, resembling a bright yellow star lying below Regulus in Leo.

Mars is hardly noticeable above the southeastern horizon shortly before sunrise, a situation which will not change much for another few months.  Mars is nearly a year away from its next opposition, at the end of January 2010, when it will be a glorious sight in next winter’s sky, as it was back in December 2007.  Mercury, like Mars, is in a poor position for morning viewing this March, rising less than an hour before sunrise at the beginning of the month.  This interval only decreases as the month progresses, culminating in Mercury reaching superior conjunction with the Sun (i.e., the Sun lies between Earth and Mercury) on the 31st.

Jupiter is slowly emerging from the morning twilight after its conjunction with the Sun back in January.  It rises in the southeast a little over an hour before sunrise on the 1st, and about 2 hours before sunrise on the 31st.   Jupiter will return to the evening sky in superb form by late summer.

 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