The Night Sky in October 2011
By Harry J. Augensen
Professor of Physics & Astronomy, Widener University
Full "Hunter's" Moon on the 11thNew Moon on the 26th
Stars and Constellations
The month of October ushers in the autumn sky while bidding farewell to the stars of summer. You will also notice that the sky gets dark considerably earlier than it did in September. (Next month, after our clocks have been switched back one hour to Standard Time, the Sun sets before 5 pm.) The "summer" right triangle is just west of overhead by 8 pm EDT in mid-October. Despite the designation, this trio of bright stars Vega (in Lyra), Deneb (in Cygnus), and Altair (in Aquila) will remain visible in the early evening sky through the end of the year. Arcturus, the fourth-brightest star in the sky and normally associated with late spring, can still be spotted as it sets low in the west-northwest, its orange color a fitting tribute to the pumpkin harvest at this time of year. Antares in Scorpius may still be glimpsed very low in the southwest after sunset, but most of the rest of Scorpius is lost in the glare of evening twilight. Following Scorpius in the southwest is Sagittarius, the Archer, followed in turn by the faint constellation Capricornus, the Sea Goat.
The notion that Capricornus represents a "sea goat" goes back to the ancient Babylonians. In Greek mythology, however, Capricornus was associated with the god Pan, a creature having the torso of a man and the legs of a goat. As a zodiac constellation (like Scorpius and Sagittarius), the Sun passes within the borders of Capricornus from about January 18 to February 14, which is about a month after it passes through the astrological sign of the same name.
As evening unfolds, the stars of autumn take center stage. Following Capricornus in the southeast is Aquarius, the Water Bearer. Just below Aquarius and low in the southeast after 9 pm EDT in mid-October is the whitish star Fomalhaut, located in Pisces Austrinus, the Southern Fish. The Great Square of Pegasus, which is actually a rectangle consisting of four stars, is situated high in the south-southeast at about this same time, and is another sure sign of autumn. Wrapped around the southern and eastern sides of the Great Square is Pisces, the Fishes, the next zodiac constellation after Aquarius.
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. Polaris actually consists of three stars, the brightest of which is a supergiant star with a luminosity of 2500 suns. It is also classed as a pulsating variable star known as a Cepheid (after the prototype in the constellation Cepheus). Such stars expand and contract in size in cycles of several days. In the case of Polaris, its pulsation cycle takes 4 days. Polaris lies at a distance of 431 light years from our solar system.
Between Pegasus and Cassiopeia lies the constellation Andromeda, the chained maiden in Greek mythology. This faint constellation contains within its boundaries the famous Andromeda Galaxy, which lies over two million light years from our solar system. The Andromeda Galaxy is often thought of as a sister galaxy to our own Milky Way, and is the most distant object visible (barely) to the naked eye. The now obsolete Y-shaped group Gloria Frederici (Frederick’s Glory) lies in the region between Andromeda, Cassiopeia, and Lacerta. It was created by Johannes Bode around 1790 in memory of Frederick the Great of Prussia, who had died a few years earlier. Its stars have since been absorbed into Andromeda and Cassiopeia.
Naked-Eye Planets In the Evening and Morning Sky
As October opens, Venus is still closely aligned with the solar orb, setting only a half hour after the Sun. By the end of the month, Venus will be setting an hour after sunset and resembling a bright yellow star very low in the west. Trick-or-treaters may be able to spot it about 30 minutes after sunset on Halloween night, if they have a clear view of the western horizon. In the coming weeks, Venus will continue to climb higher above the western horizon, and by year's end it will have emerged completely from the twilight background to be a spectacular yellow-white beacon in the western sky during the early evening hours. Hopefully Venus will not be reported as a UFO too often!
Mercury, like Venus, is immersed in the evening twilight for much of October. By the end of October, Mercury sets only about 45 minutes after the Sun, and, since it is much fainter than Venus, will be a challenge to find low in the west.
Jupiter is at its regal best this October, when it dominates the night sky (except of course for the Moon) from early evening until dawn. Jupiter resembles a brilliant cream-colored star, and is so bright that it might be initially mistaken for an airplane landing light as it stands above the northeastern horizon during the early evening hours of October. A small telescope reveals cloud bands in its atmosphere, and four bright satellites in its vicinity. Jupiter is up by around 8 pm EDT (roughly an hour after sunset) at the beginning of the month, and just before sunset on Halloween. Jupiter reaches opposition with the Sun on the 28th, when it rises as the Sun sets and sets when the Sun rises, and therefore is viewable all night. Of the planets, only Venus is brighter, but until Venus climbs out from the glare of evening twilight in the opposite part of the sky over the next few months, Jupiter will assume the lead role on the stage of the celestial theater.
Rising in the northeast at around 1:30 am in mid-October, Mars looks like a bright orange-red star in the night sky, of about the same brightness as nearby Pollux in Gemini. Right now Mars pales in comparison with magnificent Jupiter, but Mars is slowly and steadily brightening with each passing month, destined to reach its peak next March when Earth passes Mars in its orbit about the Sun.
Saturn is lost in the twilight glare at the start of October. Shortly after reaching conjunction with the Sun on the 13th, however, Saturn vaults quickly into the morning sky, and by Halloween morning it rises nearly one and a half hours before the Sun does.
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 2011 by Guy Ottewell (Raynham, MA: Universal Workshop, 2011)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/