The Night Sky: October 2009

Contents

The Night Sky in October 2009

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

Moon’s Phases in Month
  Full "Harvest" Moon on the 4thNew Moon on the 18th

The Harvest Moon is the Full Moon which occurs closest to the Autumnal Equinox. During most years the Harvest Moon occurs in September but this year it falls in early October.

Stars and Constellations

Cool, clear October nights provide the ideal stage for a parade of autumn constellations.  The stars of late spring and summer have all but vanished from the evening sky, but one notable exception is Arcturus, the fourth-brightest star in the sky.  It can be spotted as it sets low in the west-northwest, its orange-gold color a reminder of the pumpkin harvest and the leaf color of sugar maples at this time of year.  Another holdover is the "summer" triangle of Vega (in Lyra), Deneb (in Cygnus), and Altair (in Aquila), which is just west of overhead by 8 pm in mid-October. 

By 10 or 11 pm, the stars of autumn completely dominate the night sky.   Low in the southeast is the whitish star Fomalhaut, located in Pisces Austrinus (the Southern Fish).  Fomalhaut lies about 25 light years from our solar system.  Further to the east is the constellation Cetus (the Whale), marked by the moderately bright star Menkar, or alpha Ceti.  Menkar is a red giant star with a luminosity of over 100 suns and lying about 130 light years from our solar system. The Great Square of Pegasus, consisting of four whitish stars, is high in the south-southeast at about this same time, and is the most distinctive landmark of autumn nights. High in the northeast is the famous "W" shape of the constellation Cassiopeia, the Queen of ancient Ethiopia.  The "W" opens up toward Polaris, the North Star.  Between Pegasus and Cassiopeia lies the faint constellation of Andromeda, the chained maiden in Greek mythology, and just below Cassiopeia lies Perseus, the legendary hero who saved Andromeda from Cetus, the sea monster. 

Lying roughly halfway between the Great Square and Fomalhaut is is the zodiac constellation Aquarius.  The Sun passes through Aquarius from February 16 to March 11.  Aquarius is very faint, like the two zodiac constellations it lies between: Capricornus, the Sea Goat (where the planet Jupiter currently resides) to its west and Pisces (the Fishes) to its east.  This entire region of the sky, which also includes Pisces Austrinus and Cetus, is associated with water, and was even called “the Sea” by the ancient Babylonians.  British astronomer Robin Kerrod writes in his book, The Book of Constellations (London: Quarto Publishing, 2002) that the Egyptians attributed the annual flooding of the NileRiver to Aquarius.  In Greek mythology, Aquarius was most likely represented by Ganymede, son of the King of Tros, founder of the city of Troy. 

 Naked-Eye Planets In the Evening and Morning Sky 

Jupiter's prominence in the evening sky seems barely diminished since its opposition with the Sun back in August.  Slowly gliding across the southern sky during the evening hours of October, Jupiter resembles a brilliant cream-colored star, easily outshining everything except the Moon and Venus.  Jupiter remains above the horizon until around 3 pm on the 1^st; it sets less than an hour after midnight on Halloween.

Mars, moving through Gemini and into Cancer during October, is now a little brighter than the star Aldebaran in Taurus, which lies two zodiac constellations to the west.  Mars rises around 12:30 am at the beginning of October and by a few minutes before midnight on Halloween.  We are just three months away from Mars’s next close encounter with Earth in late January 2010.

Venus continues to be a magnificent beacon, sparkling with a yellow-white brilliance in the east-northeast during the pre-dawn hours.  Venus rises a few minutes before 5 am in early October, and at 6 am, only 1½  hours before sunrise, on the 31^st.  At midmonth, Venus makes a close pairing with Saturn in the morning sky.  During the closing days of 2009, Venus will vanish into the morning twilight and slowly reappear in the evening sky during early 2010. Mercury rises about an hour and a half before sunrise as October opens, and looks like a yellow star hovering low above the eastern horizon.   Mercury reaches greatest elongation with the Sun on the 6^th, when it rises around 5:30 am, or 90 minutes before the Sun.  Two days later, Mercury passes close to Saturn low in the predawn sky.

Saturn was in conjunction with the Sun last month, after having spent most of the spring and summer 2009 in the evening sky, and is still lost in its glare during early October.  It quickly emerges from the twilight in the morning sky, however, and by midmonth it rises about 2 hours before sunrise.  On the 8^th, Saturn pairs up with Mercury, and, a few days later, with Venus.  By Halloween morning, Saturn is rising a little after 4 am, or about 3 hours before the Sun. 

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.