by Geoff Chester, USNO Public Affairs | 12 September 2023 Messier 11, the "Wild Duck Cluster" in Scutum, imaged 2013 August 5 at Fishers Island, New York with an Antares Sentinel 80mm (3-inch) f/6 refractor, iOptron Cube Pro mount, and a Canon EOS Rebel T2i DSLR The Moon returns to the evening sky late in the week as her slender crescent skirts the southwestern horizon. New Moon occurs on the 14th at 9:40 pm Eastern Standard Time. The citizen-science Globe at Night observing campaign for September continues this week through the night of the 14th. As we mentioned last week, the target constellation is Cygnus, the Swan, whose brightest star, Deneb, is the northernmost apex of the Summer Triangle asterism. Cygnus lies directly overhead at 10:00 pm local time, providing ideal observing conditions for sky watchers at any location. Whether you live in the city or in rural areas far from city lights, any observations of the constellation are valuable to science. The program, which was established in the International Year of Astronomy in 2009, has been charting the visibility of the night sky to track the spread of light pollution. In that time well over 286,000 observations have been made around the world, giving a comprehensive measurement of the spread of unwanted nighttime lighting. You can help to increase awareness of this gradual erosion of our night sky by filing a report with the Globe at Night web app. We are now at the time of the year when the length of waning daylight reaches its maximum rate. As we approach the autumnal equinox we lose just over 2.5 minutes of daylight each day. Those of us who enjoy stargazing at a decent hour always look forward to this time of year. Not only do we have more nighttime hours to enjoy our pastime, we can do so in the cool air of early autumn. If you are interested in exploring the sky of late summer and fall, you have a number of opportunities to do so in the Washington, DC area this weekend. On the evening of the 15th, the Analemma Society will conduct its regular Friday public observing session at its facility at Turner Farm Park near Great Falls, Virginia. On the 16th the monthly “Astronomy for Everyone” program takes place at Sky Meadows State Park, just over an hour’s drive from the Washington metro area in Paris, Virginia. If you wish to visit a truly dark site, head out to Davis, West Virginia for the annual Blackwater Falls Star Party, which takes place at Blackwater Falls State Park from the 14th through the 16th. The showpieces of the summer sky linger in the evening hours as we move through the last week of the astronomical season. As mentioned earlier, the bright asterism known as the Summer Triangle is overhead as evening twilight ends. In recent weeks I’ve mentioned some of the treats you can find near the stars Deneb and Vega, but we shouldn’t overlook the area around the Triangle’s southernmost star, Altair. There are a number of small, obscure constellations in the area, as well as some remarkably dense Milky Way star clouds, which are well-seen in binoculars. About 12 degrees north of Altair you will encounter a small group of stars that look like an upside-down coathanger. First noted by the Persian astronomer Al Sufi in the year 964 CE, it is a popular object for small telescope owners at star parties today. Sweep some 20 degrees southwest of Altair and you will encounter a group of stars that resemble a shield. Near the bottom of the shield is a prominent fuzzy patch of light. A small telescope will resolve it into stars, and a six-inch telescope will show it in its full splendor. Known as Messier 11, its popular name is the “Wild Duck Cluster” after a particularly loquacious description by the 19th Century British astronomer Admiral William Henry Smyth. Saturn is well-placed for viewing as soon as darkness falls, glowing in the southeastern sky. The ringed planet lies in a very sparse star field among the rising autumnal constellations. It is always worth taking a telescopic look at Saturn; to me there is no other sight in the sky that is more captivating than the planet, nested in its rings, surrounded by the faint twinkles of its icy moons. Jupiter continues to make headway into the evening sky. He now rises at around 9:30 pm local time, and he soon dominates the eastern sky. Old Jove leads the parade of rising winter constellations. By midnight the first bright stars of the Great Winter Circle, Capella and Aldebaran, are above the horizon, heralding the rising of some of the brightest stars in the heavens. Dazzling Venus continues to shine in the east in the pre-dawn sky. Once you have spotted her, see how long you can keep her in view before the Sun rises. You may be surprised to still see her on clear mornings after the Sun appears.