By Peter Becker
One of the most prominent summer constellations is Cygnus the Swan. The graceful swan is a beautiful bird, and its counterpart among the stars is spectacular as well. The brighter stars form a distinct shape of a cross an is aptly nicknamed the Northern Cross. Cygnus is spread out overlapping the hazy Milky Way Band. Even if light pollution or summer haze takes away most of your view of the Milky Way, on a night without a Moon you are likely to be able to glimpse the Milky Way in this region.
In mid-northern latitudes, Cygnus the Swan rises high and passes overhead, far above the thicker haze along the horizon. The Milky Way will appear as a hazy shine right through the shape of the cross.
Deneb is the brightest star in the Swan, marking the top of the cross or when pictured as a swan, the bird’s tail. In the evening in early August Cygnus will be seen high in the east, with the cross shape on its side, and Deneb to the far left.
Deneb is a white super-giant star, one of the most luminous stars known. Its distance is uncertain but may be 3,200 light years away- its light you see tonight left Deneb around 1,200 B.C. If the Sun was replaced with Deneb, the Earth would be skimming the surface of the star (one hot ride).
The star on the far opposite end marks either the bottom of the cross figure or the head of the swan. This is Albireo, and it is a wonderful double star. Even binoculars may resolve the two stars, if held very steady; a small telescope will split the pair easily into its blue and gold components.
If you have binoculars, sweep the Milky Way Band in this region and notice the richness of the star fields. Cygnus the Swan is home to many star clusters and nebulae, because it is on the course of the Milky Way Band. Nebulae our simply vast clouds of cosmic dust or gas, principal components of the galaxy. Interstellar dust actually blocks most of the Milky Way Galaxy from our view. Dust that is not illuminated by stars appear to us as regions of blackness, punctuated by foreground stars and hiding multitudes of stars to the rear. Eyes alone, on a clear, clear night, will reveal a great apparent split down the Milky Way Band beginning at Cygnus and heading to the south. This rift is actually an incredibly long expanse of dark nebula.
Within Cygnus are several examples of emission nebulae, radiating light from mainly ionized hydrogen gas. A famous example is the so-called North American Nebula, which is not hard to imagine how it was named. The general outline shows a crude map of this continent. Next to it is the Pelican Nebula, which looks somewhat like the bird. This is the astronomical answer of laying on grassy hill and picking out shapes in the puffy clouds that cross a lazy summer’s blue sky. Try it some day.
Conveniently, Cygnus the Swan migrates with its own celestial “map” of North America.
The North American and Pelican nebulae are found just north of the star Deneb. On a dark, clear night, they may be detected with good binoculars or a backyard telescope, at low magnification.
New Moon is on August 6.
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Keep looking up!