Constellations of the Month
By Rick Raasch
Sagittarius is the happy hunting ground of the summer observer. Within it lies the very heart of the Milky Way itself, providing vistas which are unparalleled in grandeur and diversity. Our southerly latitude provides us with views unattainable by our more northerly brethren, for whom this constellation lies just along the southern horizon. Diffuse nebulae abound in this region, along with their associated open star clusters. As globular clusters orbit around the center of our galaxy, many of this beautiful class of objects are also found within its boundaries. In the present article, I will only be able to highlight objects which I found to be particularly fascinating, and will almost assuredly leave out somebodys favorite objects. The truth is, this constellation is worthy of several nights observing, and not just for Messier objects. Many beautiful non-Messier objects can be found by examining a star chart and pointing a telescope.
M-8 The Lagoon Nebula. One of the finest cluster/nebula combinations in the sky. The large, scattered open cluster lies at the eastern edge of a large, swirling cloud of nebulosity. The nebula has obvious dark lanes and looping patterns, which in long exposure photography are shown to dense star forming regions. This is a fine sight in almost any telescope, and is easily seen by both the naked eye and in binoculars.
M-20 The Trifid Nebula. This often photographed nebula is rather faint in small telescopes, but in moderate size instruments shows a circular patch of light surrounding a double star. Tis patch of light is more or less equally divided by three intersecting dark lanes meeting near its center. A fainter region of reflection nebulosity can be seen to the north.
M-17 The Omega or Swan Nebula. This is one of my favorite objects in this region. This bright nebula looks like a check mark or swan floating in a heavenly pond. It consists of a curving arc of nebulosity connected to a straighter bar shape. The bar portion shows a lot of intricate mottling and streaks. Photography shows this region to be only a small part of a larger, billowing nebulous region.
M-22 This is one of the finest globular clusters in the sky visible from northern latitudes. It is large, about 15-20' in diameter, and is rather loosely gathered, allowing us to resolve many individual stars across its face. Some consider this globular to be second only to Omega Centauri in beauty.
M-24 The Small Sagittarius Star Cloud. This is a large, disconnected portion of the Milky Way. The best view comes in binoculars, which show countless stars and some obvious dark streaks along its length. NGC 6603, which some authors claim erroneously to be M-24, lies in its northeastern section. This is a small, tight open cluster bearing no resemblance to Messiers original description.
NGC 6522 & NGC 6528 Anyone who has observed with me will not be surprised by my inclusion of these two faint globular clusters in this article. Every time I observe in the summer, my telescope is at some time pointed at these objects. They are small and moderately faint, but lie within the same field of view of a low power eyepiece in a highly populated region of the Milky Way. The longer they are observed, the more background stars become visible, producing a grainy backdrop for these two twin globulars. A great deep sky double!
NGC 6520 & B86 Another of my personal showpiece objects in Sagittarius. NGC 6520 is a small, rather tight gathering of about twenty stars placed right next to a similarly sized dark nebula, B86. The proximity of the cluster seems to accentuate the darkness of the nebula and make it appear as a hole in the sky, definitely darker than the surrounding region. This dark nebula is commonly known as the Ink Spot because of this.
Next Month: Pegasus and Andromeda
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