The Night Sky: March 2010

Contents

The Night Sky in March 2010

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

Moon’s Phases
New Moon on the 15thFull "Worm Moon" on the 28th                            

Stars and Constellations

Spring begins in the Northern Hemisphere on March 20^th at 1:32 pm Eastern Daylight Time, when the noon Sun stands exactly overhead at the Earth’s equator. Although not directly visible because of the Sun's daytime brilliance, the Sun begins March in the constellation (not the astrological sign) Aquarius, crosses into Pisces at mid-month, and remains in Pisces for the remainder of the month.  Both Aquarius and Pisces are, of course, autumn constellations, and therefore best viewed at night at the opposite time of the year when the Sun passes through them. 

The seasonal transition between winter and spring becomes apparent in the star patterns visible in the night sky as well, for the constellations of winter will over the next several weeks be fading into the evening twilight.  The star Aldebaran in Taurus and the compact star cluster Pleiades, or 7 Sisters, 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-southwest.  The twin stars Pollux and Castor in the constellation Gemini are high in the southeast, while the brightest appearing star in the night sky, Sirius in Canis Major, shines with bluish-white radiance to Orion’s lower left.  Above and to the left of Sirius is Procyon in Canis Minor. 

As evening progresses into night, the stars of spring begin to emerge from the eastern horizon.  Regulus, the brightest star in Leo, stands high in the east by 9 pm, and is one of the first spring stars to become visible after dark. Regulus lies about 78 light years from our solar system, and is intrinsically 100 times brighter than the Sun.  The name Regulus denotes "Royal," and, according to British astronomer Patrick Moore in his book, The Observer’s Year (London: Springer-Verlag, 1998), Regulus was one of the four Royal Stars (along with Aldebaran, Fomalhaut, and Antares) of the ancient Persian monarchy who were "Guardians of the Heavens." Regulus marks the lower part of what is Leo’s most distinctive feature: its "sickle," which represents the mane of the lion.  In mythology, Leo represented the Nemean Lion which was slain as one of Hercules' 12 labors. Leo is, of course, one of the twelve zodiac constellations, with the Sun passing within its borders between August 10 and September 15.  In fact, Regulus is so close to the ecliptic path that it is occasionally occulted (eclipsed) by the Moon.  

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 and, like Regulus, is intrinsically about 100 times as luminous as the Sun.  However, Arcturus lies 36 light years from our solar system, or about twice as close to us as Regulus, and so it appears brighter. The Big Dipper, which is part of the large constellation Ursa Major, is also rising in the northeast, and its handle arcs to Arcturus.  The two front stars in the bowl of the Big Dipper, Merak and Dubhe, point toward the North Star, Polaris.

Naked-Eye Planets In the Evening and Morning Sky 

Mercury passes through superior conjunction with the Sun on March 14th and therefore is unobservable for much of March.  Toward the end of the month, however, Mercury pops up in the western sky at dusk, and by the 31st it sets nearly one and a half hours after sunset.  Venus, which was in conjunction with the Sun back in January, is just beginning to emerge from the evening twilight.  Venus sets only an hour after sunset as March opens, and an hour and a half after the Sun by the 31st.  If there are no trees or houses to obscure the view, you may be able to spot brilliant Venus shining low above the western horizon.

Mars was closest to Earth and at its brightest back in late January, and it still outshines Saturn and nearly all the other stars in the March night sky.  Mars resembles a bright, copper-colored star high in the northeast during the evening, and stays in view until the wee hours of the morning.  As March begins, Mars lies about 72 million miles from Earth, which is about 10 million miles further away than it was at opposition.  By month's end, the Earth-Mars distance will have grown to just over 93 million miles, or the same distance as the Sun is from Earth.  Correspondingly, as March opens, Mars’s brightness has faded to one-half of what it was at opposition, and by month's end it will have dimmed to nearly one-fourth the opposition value and have the same brightness as nearby star Capella.  

Saturn resembles a bright yellow star as it rises above the eastern horizon in late evening.  At the beginning of March, Saturn rises by 7:30 pm, and on the 21st it reaches opposition with the Sun, rising as the Sun sets and setting as the Sun rises.  Saturn is also closest to Earth this month, though still fainter than Mars.  Continuing its residence in the constellation Virgo, Saturn, with its magnificent ring system, is always a wonderful sight in the telescope.  Jupiter, which was in conjunction with the Sun on the last day of February, is still too close to the Sun to be observable.

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.