The Sky This Week, 2013 September 3 - 10
NGC 869 & NGC 884, the "Double Cluster" in Perseus
The Moon returns to the evening sky this week, waxing through her crescent phases as she skirts the southwestern horizon. New Moon occurs on the 5th at 7:36 am Eastern daylight Time. Look for a beautiful pairing of the Moon and bright Venus on the evening of the 8th. The two objects will be just under two degrees apart in the deepening twilight, which should provide a nice photo opportunity for budding astrophotographers. The following evening you’ll find a somewhat fatter Moon about five degrees east of Saturn.
The early evening hosts Venus and Saturn during the twilight hours. Once the sky is fully dark, we don’t see any other naked-eye planets until well after midnight. Venus is quickly closing the gap with Saturn as both planets attempt to keep pace with the advancing Sun, but only Venus has the stamina to stay ahead. Neither planet offers much for the telescopic observer right now as both planets are close to the horizon, which means that we have to observe them through dense turbulent layers of air that muddy the fine-structure details of these distant worlds. However, it’s still worthwhile looking at them through binoculars, particularly when the Moon comes to pay her calls.
The absence of the Moon and bright planets in the evening certainly doesn’t limit what you can see with a small telescope. The Summer Milky Way abounds with sights to keep you entertained all evening long. If you’re stuck under the bright lights of the city or close-in suburbs there are plenty of colorful double stars to vie for your attention. One of the easiest to observe is Albireo, which lies smack in the middle of the Summer Triangle, which in turn straddles the meridian at around 9:30 pm. Viewed with the naked eye, Albireo is an otherwise nondescript star that marks the head of Cygnus, the Swan (the bright star Deneb, one of the "apexes" of the Summer Triangle, marks the Swan’s tail.) Turn any small telescope toward Albireo, though and you’ll see two superbly tinted stars. I like to call this pair the "Navy Double" since it mimics the blue and gold colors of our Service. This pair is best seen in small-aperture telescopes; large instruments tend to wash out the delicate tints of the component stars. Albireo is a physical binary star whose components orbit each other with a period of about 214 years. If you’d like a bit more of a challenge, move your telescope toward the brightest star in the Triangle, Vega. Just to the east of the star you’ll see a pair of stars in your finderscope. If you look at this pair, known as Epsilon Lyrae, with a telescope of three or more inches of aperture you’ll see that each of the components is itself a close double star, giving this quadruple system its popular name of "The Double-Double". If you enjoy darker skies, prowl the Milky Way at low power for many of the star clusters and nebulae that are embedded within its bounds. One of my favorite objects to examine with any type of optical aid may be found high in the northeast by 11:00 pm. Located just to the southeast of the W-shaped constellation of Cassiopeia in the heart of the Milky Way, the "Double Cluster" is visible as an elongated hazy patch with the naked eye under dark skies. Binoculars will resolve the brighter stars of the cluster, but once again the view through the small telescope is the best. Each cluster is made up of a few thousand stars, with the brightest members numbering among the most intrinsically brightest stars in the sky. Most of these stars are bluish in tint, but careful observation will reveal a number of red supergiant stars scattered between them.
Jupiter now rises just before 2:00 am, so he’s still best observed right before sunrise. While I haven’t yet had a chance to view him this year I’ve heard from a number of my observing friends that Old Jove is putting on a good show so far. His equatorial cloud belts are continuing to teem with activity as they did last year, and the famous Great Red Spot seems to be gaining prominence in both form and color. This all bodes well for a great viewing season once Jupiter reaches the evening sky.
You’ll also find ruddy Mars in the east if you’re up looking at Jupiter before dawn. The red planet forms one apex of a diamond along with Jupiter, the star Procyon, and the Twin Stars of Gemini, Castor and Pollux. Mars isn’t much to look at through the telescope right now, with his disc showing little more than a small pinkish dot. However, this is a great week to watch him through binoculars. On the mornings of the 8th and 9th he’ll be passing directly in front of the so-called "Beehive" star cluster in the constellation of Cancer, the Crab.