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Harvesting the Autumn Skies: Be prepared to gaze in wonder upon September's diaphanous delights.

In September you have to observe right after nightfall to catch the Sagittarius Milky Way at its highest. But there's more than just our galaxy's glow to enjoy on September evenings. Those skies offer us a generous helping of virtually every kind of deep-sky object possible.

September's star clouds and diffuse nebulae Many patches of brighter naked-eye radiance shine along the so-called summer Milky Way. Six that are both prominent and well-known are: the Cygnus Star Cloud, the Scutum Star Cloud, the Large Sagittarius Star Cloud, the Small Sagittarius Star Cloud (M24), the Lagoon Nebula (M8), and the big open star cluster M 7. The next of these bright naked-eye patches is an impressively intense one that seems to have escaped naming and therefore fame. A few years back in this column I dubbed it both the Gamma Scuti Star Cloud and also a name befitting its mysteriousness: "the Seventh Glow."

The Seventh Glow forms a compact equilateral triangle with two famous Messier nebulae that require optical aid to see properly. One of these is M16, the Eagle Nebula or Star Queen Nebula, of Hubble Space Telescope photographic fame with its "Pillars of Creation." The other is Ml 7, most often called the Omega Nebula, but also variously known as the Swan Nebula, Horseshoe Nebula, and Checkmark Nebula (see Howard Banich's Going Deep column, S&T: Sept. 2017, p. 57). The triangle of M16, M17, and the Seventh Glow is only about 2 1/2[degrees] to a side and yet each of the three is in a different constellation--Serpens (M16), Sagittarius (M17), and Scutum (the Seventh Glow star cloud),

September's strip of planetary nebulae and a poignant supernova remnant. I always find it remarkable that the two most famous and prominent planetary nebulae, along with two other notable planetaries, are all located within a surprisingly small strip of the heavens. M57, the Ring Nebula in Lyra, and M27, the Dumbbell Nebula in Vulpecula, lie on a line with the renowned double star Albireo, or Beta ([beta]) Cygni, which shines about midway between them. Considerably farther to the southeast are the other planetaries, both in Aquarius: the small, intense Saturn Nebula (NGC 7009) and the great-in-total-brightness but huge and thus low surface brightness Helix Nebula (NGC 7293). Of the sky's finest planetaries, others can be found in this general region of the heavens--for instance, NGC 6826, the Blinking Planetary, in Cygnus.

Near the other wing of Cygnus, the Swan, is a stellar aftermath more ancient than the planetary nebulae, one formed from a much mightier stellar demise. It's a supernova remnant, its arcs and shreds of radiance forming the roughly 3[degrees]-wide Cygnus Loop. The easiest section of the Loop to find is NGC 6960, the Veil Nebula.

September's globulars galore --but also key open clusters and a galaxy. Summer is the great season of globular star clusters, but on September evenings every major globular from late spring's M3 and M5 to autumn's M15 and M2 is reasonably well placed. Fine open clusters for September evenings include Mil (midway up the sky); M6, M7, and M25 (fairly low but quite visible); M39 (high); and the Double Cluster in Perseus (still pretty low but climbing). Summer and winter are poor seasons for galaxies other than our Milky Way, but by September the visually greatest external galaxy, M31, is high enough for good evening views.

Red, double, variable stars, and more September brings us great views of red Mu ([mu]) Cephei (Herschel's Garnet Star); Epsilon ([epsilon]) Lyrae (the Double Double) and Albireo; Delta ([delta]) Cephei. and Rasalgethi (both stars that are fascinating variable stars and colorful doubles). There's a dearth of very bright stars at the time of our all-sky map: The only ones of 1st-magnitude or brighter are Arcturus, Vega, Altair, Deneb, and Antares. But at least this year Venus, Jupiter, Saturn, and Mars all help brighten our September evenings.

Contributing Editor FRED SCHAAF welcomes your letters and comments at fschaaf@aol.com.

Caption: NGC 6960, also known as the Veil Nebula, is ' part of the Cygnus Loop supernova remnant.
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Title Annotation:Under the Stars; Sagittarius Milky Way
Author:Schaaf, Fred
Publication:Sky & Telescope
Date:Sep 1, 2018
Words:680
Previous Article:Planetary Almanac.
Next Article:Autumn Arrives: As summer gives way to fall, lengthening nights offer planet-spotting from dusk to dawn.
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