by Geoff Chester, USNO Public Affairs | 01 October 2024 Messier 31, the Great Andromeda Galaxy, imaged 2017 October 21 from Great Meadow, Old Tavern, Virginia with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor and a Canon EOS Rebel T2i DSLR The Moon waxes in the early evening sky this week, appearing as a thin crescent low in the western sky after New Moon, which occurs on the 2nd at 2:49 pm Eastern Daylight Time. Luna’s burgeoning crescent slinks along the southern horizon, passing a few degrees to the southeast of bright Venus in evening twilight on the 5th. She ends the week some two degrees east of the bright red-hued star Antares in Scorpius on the evening of the 7th. At this time she will be less than half a degree north of the second-magnitude star Tau Scorpii. October is a month of transition for the night sky. We still have summer’s bright constellations to enjoy in the early evening, but autumn’s signature constellations are becoming prominent in the eastern sky as midnight approaches. As evening twilight ends the bright stars of the Summer Triangle are prominent overhead. Vega, Deneb, and Altair have just passed to the west of the meridian, while Scorpius sets in the southwest. The Scorpion will soon be followed by the “teapot” asterism formed by the bright stars of Sagittarius, and the densest of the summer Milky Way’s star clouds will begin to sublimate into the horizon haze. To the south and east we find a relative dearth of stars. The constellations of Capricornus, Aquarius, and Pisces offer few bright stars to view, but higher in the east you should be able to easily find a large square asterism that forms part of the constellation of Pegasus, the mythical Flying Horse. To the northeast is the diminutive, W-shaped outline of Cassiopeia. As the night passes, these patterns gain more prominence, and offer a chance to see a truly far-out object. Between Cassiopeia and the star Alpheratz that marks the northwest corner of the Square you will find a “chain” of stars trending to the northeast. From a dark location you will see a fainter chain diverging from Alpheratz. These are the chains that bound Andromeda, the beautiful daughter of Cassiopeia, to a rock as punishment for the latter’s boastfulness. If you look carefully from a dark site, you will see a small smudge of light about seven degrees northwest of the third star in the brighter chain, Mirach. This is the famous Andromeda Galaxy, the closest large galaxy to our Milky Way. At a distance of 2.5 million light years, this is the most distant object visible to the unaided eye. The Andromeda Galaxy is best seen in binoculars or a low-power telescope. It appears as a softly glowing elongated streak at low magnifications; higher powers show a gradual increase in brightness toward the center, but the glow remains amorphous. One early observer, Simon Marius, described its appearance in 1612 as “the light of a candle shining through horn”. It was first described by the Persian astronomer al-Sufi in 964 CE. Follow the Milky Way up to Cassiopeia to spot some of the bright star clusters that lie along the galactic plane. About seven degrees to the east of the “W”, embedded in a spectacular Milky Way star cloud, is the well-known “Double Cluster” of NGC 869 and 884. They are easily seen in binoculars, but they are truly spectacular to view through a telescope. Located about 7500 light years from us, the clusters’ brightest stars are some of the most luminous in the Galaxy, blazing with over 100,000 times the power of the Sun. The bright planet Venus is steadily climbing in the western sky as evening twilight fades. She is still best seen about 20 minutes after sunset when her bright white glow contrasts with the red of the twilight horizon. Look for the waxing crescent Moon below the dazzling planet on the evening of the 5th. Saturn is easy to find in the southeastern sky as evening twilight fades. He’s nowhere near as bright as Venus, but he las little competition in this part of the sky. The closest bright star to the ringed planet is Fomalhaut, some 20 degrees to the south. Late night skywatchers will find the bright glimmer of Jupiter cresting the eastern horizon shortly before 11:00 pm as the first of winter’s bright constellations, Taurus and Auriga, come into view. Old Jove is situated between the “horns” of Taurus, where he will remain for a couple of weeks. He will reach the first stationary point of the current apparition on the 9th; he will begin to slowly move toward the bright star Aldebaran as he approaches opposition in early December. Mars spends the week crossing through the stars of Gemini. You will need to get up before dawn to get a good view of his ruddy glow. By mid-January, though, he will be in the sky all night, outshone only by Jupiter and Venus.