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Out There

Deep Sky for July

Mark Wagner


Here are three images of the Crescent Nebula, NGC6888. Top, photographic image by Ray Gralak. Middle, a sketch by Bernd Nies. Bottom, a sketch through an 8-inch newtonian by Robert Kerwin.

 

This month the best time to observe deep sky objects in the evening skies will be between July 6th and 13th. I'll concentrate on objects in Sagittarius, Cygnus, Vulpecula and Lyra that are well placed for observing during the two hours beginning at astronomical dark.

Start in Sagittarius with an easy object that performs well in most any telescope. M22 is one of the most rewarding globular clusters in the northern sky. It appears large and coarse compared to other popular globulars, and can be seen with binoculars or a finderscope. To find it scan 2 1/2 degrees ENE of Kaus Borealis, the top star in the Teapot. Many other interesting objects dot the area. Visit M28 and NGC6642, two other globulars close to M22. For more variety, from a dark sky, try the globular Palomar 9 just off nu Sagittarii. This entire area around Sagittarius and Scutum is so rich it is a great place to leisurely sweep with binoculars or a rich field telescope.

For a dark sky challenge object try Barnard's Galaxy, NGC6822. Find the area by starhopping from xi Sagittarii to rho Sagittarii, then extend beyond rho the same distance. See if you are able to glimpse some of the brighter sections of this low surface brightness galaxy. This is a tricky object, some describing it as no more than a subtle change in contrast in their eyepiece. Others detect H-II regions (like the Orion Nebula). It can actually be more easily seen in astronomical binoculars than with the narrower field and higher magnifications of a telescope. I usually look for the planetary nebula NGC6818 "The Little Gem" as a nearby landmark. Barnard's Galaxy is less than 1 degree SSW.

A good binocular object that responds well telescopically is M27, the famous Dumbell Nebula. Like NGC6818, M27 is a planetary nebula. Compare the two to see how varied planetaries can be. The Dumbell is a treasure of detail, especially in a dark transparent sky enhanced with an Ultra High Contrast (UHC) filter. Also try an O-III filter if you have one and note the difference. Look too for the central star, visible at magnitude 12.5. The Dumbell is easy to find. I think of its position as the "missing star" in a parallelogram formed by beta, gamma and epsilon Cygni. With an optical finder you'll have no trouble locating it as a hazy smudge.

While in the area use your binocular and move 8 degrees W to take in the "Coathanger". a busy open cluster (a.k.a. Collinder 399). Enjoy the unusual straight edge along the northern side of the cluster. With your telescope, see if you can find NGC6602, a magnitude 8.8 open cluster at the eastern end of Coll 399.

How about another planetary nebula? NGC6826 is called the Blinking Planetary. With modest magnification you will see the small ball of nebulosity. Stare directly at the center of the object and the nebulosity disappears, replaced by the central star. Look away from the star and the nebulosity pops out again! Locate it by moving 1 degrees W of theta Cygni, at the bend in Cygnus' western wing. Note too the nice equal double star 16 Cygni about 30" W of the planetary. In an undriven scope you can put the double star in the field and watch the planetary drift in. In a good dark sky with some aperture a pair of small galaxies can be seen just off 16 Cygni to the NNW.

The next object can be found classified as a supernova remnant, emission or reflection nebula. But I think of NGC6888 as a planetary nebula. It contains WR136, a super hot Wolf-Rayet star. The hot star is tearing apart the shell of material we see as nebulosity in moderate apertures under dark transparent skies. This egg shaped nebulous shell is known as the Crescent Nebula, and is striking in its beauty and detail. Note the brighter portions of the shell and the extension leading in toward the central star. Locate it by moving from gamma Cygni one third the way to eta Cygni. This egg shaped wreath of nebulosity responds well to UHC and O-III filters. Don't overlook the myriad of other deep sky wonders in the area - dark nebulae, planetaries, open clusters, reflection and emission nebulae - what a rich area!

We'll finish with epsilon Lyra, the famous "Double Double." Sharp eyes can split the main pair without optical aid. With optical aid the main pair are easily observed. Increasing magnification resolves the two stars into pairs. Two double stars of nearly equal brightness and separation in a single field of view!

Next month will include objects in Capricornus, Equuleus, Delphinus, Vulpecula, western portions of Aquarius and Pegasus, eastern Cygnus and western Cepheus. If you have suggestions or requests e-mail them to me at the address below.

This article is not intended to list just well known objects, but more a variety of interesting ones. To generate a more complete list of objects for this month, visit: http://www.messier45.com/cgi/tvo/listgen.cgi on the Internet. For July I used R.A. coordinates of 18.30 to 20.30 and declination -40 to +90.

If you are interested in trying or improving your deep sky observing, find me at Houge Park or email me. There is a very active contingent of deep sky observers in the area that are friendly, have a wide range of equipment, and are available to help beginners learn their way around.

 


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