Our Delphinus and Sagitta are two of the 88 official constellations; the Coat Hanger is not. Spot all three high in the southeastern sky this week.
Two of my favorite constellations of late summer are two of the smallest in the whole sky. They aren't big and showy star patterns with lots of bright stars like Orion or the Big Dipper, but are, instead, small and compact and easy to spot only because of their distinctive shapes. They are Delphinus, the Dolphin, and Sagitta, the Arrow. The Dolphin and the Arrow are neatly tucked in under the wing of the nearby constellation of Aquila, the Eagle, marked by its bright star Altair.
To locate these two tiny constellations, go outside at about 10 p.m. and look high up in the southeastern sky. There, you should spot the three bright stars marking the corners of the Summer Triangle:Vega, nearly, straight up; Deneb, fainter and to the northeast; and Altair, to the southeast of Vega. Just east of Altair, you can spot the small diamond-shaped pattern of Delphinus, the Dolphin. The four main stars form the head and body of the dolphin, and a fifth star, off to the lower right, marks his tail. You can just about cover the entire constellation of Delphinus with your thumb held at arm's length. Our Delphinus, the Dolphin, also is popularly known as "Job's Coffin," suspended halfway between Earth and heaven, but it doesn't take a lot of imagination to see a little dolphin there, jumping up out of the celestial sea.
Just west of Delphinus, and equidistant from Delphinus and Altair, is Sagitta, the Arrow. Two stars form the shaft of the arrow, and a closely spaced pair of stars marks the feathers, or fletching, on the end of the arrow. Mythologically speaking, this celestial arrow might be a wayward shot from the bow of Sagittarius the Archer, far to the south.
Moving from Delphinus to Sagitta and then continuing in the same direction about half as far, you will come to a small fuzzy patch of light sitting in a dark portion of the Milky Way. This is not a constellation, but is a tiny asterism called Brocchi's Cluster, named for amateur astronomer D. F. Brocchi. If you have a pair of binoculars handy, aim them at the fuzzy spot to see why this delightful little asterism is nicknamed "The Coat Hanger Cluster." Its 10 brightest stars are arranged in the unmistakable shape of a coat hanger, complete with hook on top. Once considered to be a family of stars moving together through space, astronomers are now convinced that the stars of the Coat Hanger Cluster are unrelated and that this remarkable arrangement is completely by chance.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College's Alpine Campus. He is an avid astronomer whose photographs and articles have been published on the Web sites of CNN.com, NASA's "Astronomy Picture of the Day" Web site, Spaceweather.com, Space.com, Discover.com, MSNBC.com, NationalGeographic.com, and in Sky & Telescope, Astronomy, Night Sky, Discover and WeatherWise magazines. His "Celestial News" article appears weekly in the Steamboat Pilot & Today. His "Cosmic Moment" radio spots can be heard on local radio station KFMU.