This is Dudley Observatory’s Skywatch Line for Friday, September 28 through Sunday, September 30, written by Sam Salem. On Friday, the Sun rises at 6:50am and sets at 6:42pm; the waning gibbous Moon sets at 10:16am and rises at 9:00pm. Late on Friday evening, spot the Pleiades upper left of the Moon. Try to locate Pleiades’ tiny dipper pattern standing on its handle. On Saturday night, the waning gibbous Moon slowly drifts through the Hyades cluster in constellation Taurus. As it exits the cluster, the lunar disk passes within ½ degree, one Moon diameter, of the constellation’s brightest star Aldebaran. The Moon is nearest Aldebaran around 2am on Sunday Morning.
Venus is at its peak brilliancy of magnitude –4.8, shining very low in the west-southwest after sunset. It sets in late twilight. Venus sits down to Jupiter’s lower right. Their separation remains steady this week at 14 degrees. In a telescope Venus is a crescent, about 25% sunlit and 41 arc-seconds tall. Mars, in southern constellation Capricornus, fades from magnitude –1.5 to –1.3. It shines highest in the south soon after dark and sets around 2am. Jupiter, in constellation Libra, shines at magnitude –1.8 ever lower in the southwest in twilight, upper left of Venus. Saturn is already at the meridian when the Sun sets. Saturn sits in constellation Sagittarius, low in the south. However, Saturn’s magnificent rings will be apparent. The ring system, measured tip to tip, currently appears about as wide as Jupiter’s disk. The rings are tilted toward Earth by an angle of 26 degrees, which is only one degree shy of maximum. This permits easier sightings of the 4,700-kilometre-wide Cassini’s Division gap that separates Saturn’s two brightest rings. During moments of steady seeing, the threadlike feature is visible even in a 60mm refractor.
This weekend look for the loneliest star, Fomalhaut, the bright star located in a region of the sky that contains only very faint stars. Fomalhaut is a bright star in the constellation Piscis Austrinus, the Southern Fish. It is bright enough to be seen on a moonlit night. Fomalhaut rises at 7:26pm and sets at 3:24am, reaching transit altitude of 18 degrees south before midnight on Friday. No other bright star sits so low in the southeast at this time of year. Fomalhaut sits close the southern horizon until well after midnight on these fall nights. Fomalhaut is the brightest white star in an otherwise empty-looking part of the sky. The star is sometimes called the Lonely One, the Solitary One, or sometimes the Autumn Star. Fomalhaut is the 18th brightest star in the sky. The Arabic name, Fomalhaut, means “mouth of the fish” or whale. In 2008, Fomalhaut became the first star with an extrasolar planet candidate imaged at visible wavelengths. The image was published in the journal Science in November 2008. Fomalhaut is the third-brightest star known to have a planetary system, after the star Pollux in the constellation Gemini and our own Sun.