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The Sky This Week, 2015 September 15 - 22

Share the Moon with friends and neighbors.
Messier 11, the "Wild Duck Cluster"
Imaged 2015 August 15 with a Canon EOS Rebel T2i DSLR, 80mm f/6 Antares Sentinel refractor,
25 90-second subframes @ ISO 3200 at Fishers Island, New York

The Moon returns to the evening sky this week, waxing from a slender crescent to First Quarter, which occurs on the 21st at 8:59 am Eastern Daylight Time. Luna courses through the southern reaches of the ecliptic, passing just over two degrees north of the second-magnitude star Zubenelgenubi on the 17th and a similar distance northwest of golden Saturn on the 18th. On the 19th skywatchers around the world will take part in the annual International Observe the Moon Night, an evening set aside each year to promote observation and appreciation of our natural satellite and its connection to planetary science. I often say that the Moon is "looked over, then overlooked" by novice telescope users, but studying the various formations on Luna’s battered surface can become a lifelong passion, and almost any telescope will provide stunning views of the only other place in the solar system that humans have visited. There are several places to participate in this event in the Washington area. The National Air & Space Museum’s observatory will be open that evening, and astronomers will have telescopes set up to observe at the Arlington County Planetarium. Farther afield, the Northern Virginia Astronomy Club will host public observing sessions at C.M. Crockett Park near Midland, Virginia and Sky Meadows State Park near Paris, Virginia. If you own a telescope, set it up in your neighborhood and hold an impromptu Moon party for all of your neighbors!

You can still enjoy relatively dark skies early in the week before the Moon begins to blot out the fainter stars. The summer Milky Way is prominently placed overhead by 9:00 pm, offering an array of targets for binoculars and small telescopes. It is hard to describe the sight of vast numbers of stars that reveal themselves in the misty glow of the Galaxy’s softly glowing clouds. Some of my favorite views are those I’ve had with my 80-millimeter (3.1-inch) wide-field telescope at a modest magnification of about 20X. In addition to the clouds of stars, there are also voids where scarcely a star can be found. Interspersed are bright knots of light betraying the location of a star cluster or glowing gaseous nebula. One of my favorite targets can be found halfway between Altair, the southernmost star in the Summer Triangle, and Kaus Borealis, the star that marks the top of the "Teapot" asterism in Sagittarius. In the midst of one of the Milky Way’s densest star clouds is a fuzzy patch of light which a small telescope reveals as a wonderful star cluster known as Messier 11. This cluster is popularly known as the "Wild Duck Cluster" thanks to a wonderful description penned by British amateur astronomer W.H. Smyth in his "A Cycle of Celestial Objects" published in 1844. This book, with descriptions of over 850 double stars, star clusters, and nebulae, was the first observing guide intended for amateur astronomers. It has been reprinted many times, most recently in 1986, and is still a wonderful companion at the eyepiece.

Saturn gets a visit from the waxing crescent Moon on the evening of the 18th, and the ringed planet still puts on a good show in the early evening hours. Lately I’ve been observing Saturn in twilight about half an hour after sunset. This gives me about an hour of relatively stable air before Saturn begins to slip into the thermal currents near the southwest horizon. Saturn is the only bright planet currently visible in the evening sky, so take advantage of him while you still can.

The rest of the naked-eye planets may be found in the east before dawn. You’ll have no trouble spotting Venus, who reaches her greatest brilliancy on the 21st. Closer to the horizon is Jupiter, gradually emerging from his recent conjunction with the Sun. In between you’ll find ruddy Mars, currently a second-magnitude object. The red planet spends the week closing in on the bright star Regulus in Leo, the Lion. He’ll pass just south of the star on the mornings of the 24th and 25th. Watch these planets over the next month. They will be joined by fleet Mercury and undergo a number of interesting conjunctions during that time.


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