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Summer in the Wind Rivers: A Deep-Sky Cornucopia

An article I wrote for a club newsletter in September, 1994.

Every year, I make a pilgrimage. Not to the peculiarly artificial altars made by humans, but rather to the skies of the western United States -- dry, high lands not plagued by the aerosol haze that fills Illinois during the summer.

The Wind River mountains, center of a major wilderness area and containing the highest peak in Wyoming, are a playground for naturalists of all sorts. Hikers and backpackers have hundreds of peaks, valleys, and canyons to explore; fishers have some of the finest lakes in Wyoming. Canoeists, birders, and wildlife spotters all have abundant opportunities. Finally, astronomers have some of the finest skies in the West to explore. With the aid of my 10" reflecting telescope, I set to work as soon as the Sun sets. A few short tests and setup procedures later, I am ready to go.

As darkness falls, a few familiar faces appear out of the sky. Jupiter, among the brightest, still shows a conspicuous scar from the Shoemaker-Levy impact nearly a month before. In the 10", the large spots seen three weeks earlier have begun to form a new belt, rivaling the two familiar equatorial belts.

With twilight rapidly receding, I begin exploring the wealth of deep-sky objects, rendered apparent by the clear desert skies. I star first with several showpiece objects, one which are impressive from any location, but become even more so under the Wyoming blackness. My first target is the old standby from club meetings, the cluster M13 in Hercules. Partially resolved even in twilight, M13 bursts with new life in full darkness. Not only is the entire cluster well resolved even at moderate magnification, but it is also surrounded by an enormous faint halo of stars, ones scarcely visible from other locations. The halo, in addition to making M13 seem much larger than usual, adds a sense of great depth to the cluster.

Since a bright object like M13 turned out even better than expected, I started on to more challenging sights. Cygnus, flying along the stream of the Milky Way, is home to several. A famous example is the Veil Nebula, an ancient supernova remnant. In the 10", the explosion can almost be imagined, as one arc of the nebula breaks up into numerous small filaments, too complicated to draw, and small pieces of nebular glow appear between the two main arcs.

The star clusters of summer fill the southern sky. I visit several old friends -- M11, a giant, bright collection of stars near Aquila, and M22, a gigantic globular cluster that, in such pristine skies, easily rivals M13 for splendor. Nevertheless, a particular favorite of mine lurks a bit off this beaten track, in the Milky Way near Cassiopeia. NGC 7789, surprisingly little known among amateur observers, comes into its own under the Wyoming night. A dense cluster of stars, NGC 7789 is surprisingly irregular in places. Dark bands, regions of sky with fewer stars than usual, sweep through the cluster, making it take on the appearance of a large flower with broad, curved petals outlined by stars. Nearby is an interesting pair of objects: an open cluster and a galaxy, both nearly the same apparent size, but differing enormously in true distance.

As stars slowly wheel across the sky, the "summer" stars begin to sink in the west, making way for the constellations of autumn. Embedded among these are more spectacles. M31, the Andromeda galaxy, is already impressive even to the naked eye. Easily larger than it appears from the city, it appears as a huge oval whose edges seem to fade gradually into background skyglow. In the 10", the core of the galaxy is split from the outer arms by two massive dark lanes. Seemingly between the two lanes is a giant bright spot, a massive star cloud inside the galaxy itself.

M33, another spiral galaxy broadly similar to Andromeda, is also an impressive sight. Despite its enormous distance -- even farther away than M31 -- M33 is nonetheless visible as a faint spot even without the telescope, and in fact appears larger to the naked eye here than M31 does from most places in Illinois. In the telescope, M33 splits up into a clear spiral, with two giant arms of stars set among a blotchy, irregular central core. A giant bright spot appears at the end of one of the arms -- a nebula much like the famous Orion Nebula, but much larger in true dimensions.

Having seen several objects with exceptional clarity, I make a short check of how dark it actually is. Picking a convenient region of sky -- a small open space near Vega -- I make a quick sketch of all the stars I can see there, for comparison. Aware of the normal limits for viewing dim stars, I match stars on my chart with ones in a catalog. The skies here indeed are excellent; the faintest stars I have drawn are magnitude +7.3, less than half as bright as on a typical summer night in Illinois.

Eventually, over two nights, I visit another twenty or so spectacles of the deep-sky world. Unfortunately, the fine summer of the Wind Rivers is notoriously unpredictable; summer sunshine alternates rapidly with violent thunderstorms, and I am unable to see any more. There is always next year, and my choice of locations -- in Wyoming alone, the Wind Rivers are just one of hundreds of impressive sites for the deep-sky visitor.

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