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The Sky This Week
U.S. Naval Observatory's Weekly Blog
Longer Nights, Darker Skies
by Geoff Chester, USNO Public Affairs
20 September 2022
NGC 6960, the "Witch's Broom Nebula" in Cygnus, imaged 2022 August 13 from Alexandria, Virginia
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor telescope, Optolong 3-channel narrow-band L-eNhance filter,
and a ZWO ASI183MC CMOS color imager. It is the western part of a large supernova remnant, and is one of the deep-sky show pieces of Cygnus.
The Moon greets early risers this week, edging closer to the Sun as she wanes among the first constellations of spring. New Moon occurs on the 25th at 5:55 pm Eastern Daylight Time. Use binoculars on the morning of the 21st to spot the “Beehive” star cluster just south of Luna’s crescent.
The autumnal equinox occurs on the 22nd at 9:04 pm EDT. This is the moment when the center of the Sun’s disc crosses from the northern to the southern hemisphere of the sky, marking the beginning of astronomical autumn. Starting on the 26th days will be shorter than nights until March 17, 2023.
Globe at Night
citizen science star observing program continues this week. Once again the target constellation is Cygnus, the Swan, which crosses overhead at around 9:00 pm local time. Begin your observation by letting your eyes adapt to darkness for ten to fifteen minutes, then locate Deneb, the Swan’s brightest star. The Swan’s body runs toward the middle of the Summer Triangle asterism where it ends at the star Albireo. If you have a small telescope, stop at this star and enjoy the telescopic view. You will be rewarded with a wide pair of stars colored blue and gold. For this reason I like to call it the “Navy Double”. Located about 400 light years from us, it is one of the most striking double stars in the sky. There is debate as to whether the pair form a true binary system or if they form an “optical double, where two stars just happen to line up along our line of sight. On a clear autumn night from my suburban yard I can usually see five of six of the Swan’s principal stars, but darker locations will reveal many more, along with a background of a bright Milky Way star cloud. You can compare your view of the constellation with the charts on the
Globe at Night web app
and report your results there. Your observations will add to the over 13,000 other skywatchers who have contributed to this international program.
Finding dark skies to see the splendor of the summer Milky Way is becoming increasingly difficult if you live near major metropolitan areas. The International Dark Sky Association estimates that as many as 90 percent of the world’s population has never seen the subtle glow of our home galaxy. Here in the Washington, DC area we are fortunate to have a few public-accessible sites where we can enjoy darker skies, and this weekend there will be two events that you can attend to do so. On the evening of the 24th the Northern Virginia Astronomy Club will host its annual
Star Gaze at C.M. Crockett park near Catlett, Virginia
. On the same night the monthly
Astronomy For Everyone
program will be offered at Sky Meadows State Park near the town of Paris, Virginia. Sky Meadows was recently named an International Dark Sky Park, and is one of the closest such locations to any major city.
These “star parties” are a great way to learn about the fun that amateur astronomy has to offer. Here you will have the opportunity to view a wide variety of celestial objects through telescopes both large and small. Amateur astronomers are more than happy to share their views of the cosmos, and this time of the year we have an astonishing variety of things to view. The planets Jupiter and Saturn represent our solar system, while the summer Milky Way offers numerous star clusters, glowing gaseous nebulae, and mysterious dark patches that are striking for their seeming lack of stars. As the constellations of autumn take the stage we have a window to distant external galaxies, including the famous Andromeda Galaxy, which is the most distant object that is visible to the unaided eye.
The planet Saturn is now visible in the southeastern sky as evening twilight ends. This distant world never ceases to amaze people who see it in a telescope for the first time. The planet floats like a small pearl suspended in its surrounding rings. Scattered nearby are several of its small icy moons as well as its largest moon Titan, the only planetary satellite known to have a dense atmosphere. Those of us who own telescopes are used to people accusing us of showing a picture of the planet, but rest assured you are looking at the real thing!
Jupiter appears as a beacon in the eastern sky shortly after sunset. Old Jove reaches opposition on the 26th, when he rises at sunset and sets at sunrise. This is one of Old Jove’s close oppositions, which occur about every 12 years. The planet’s apparent disc will be about as large as it ever appears from our earthly perch some 591,295,250 kilometers (367,413,835 miles) above his turbulent cloud tops.
Mars rises just before 11:00 pm. You will find him high on the ecliptic among the bright stars of the Great Winter Circle. Your best time to view him is still just before morning twilight, when he will add his ruddy glow to those of the stars Aldebaran and Betelgeuse.
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