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Utah Skies: Summer Triangle In The Fall

Tom Westre

In astronomy an asterism is a group of stars that form an image but is not a constellation. The Big Dipper is a common asterism. It is made of seven stars, four forming the bowl and three forming the handle. But it is part of the larger constellation called Ursa Major, or the Big Bear.

The Summer Triangle is another asterism. It consists of three bright stars, Vega, Deneb, and Altair, that are part of other constellations. Vega is the brightest star in the constellation Lyra, the harp, and due to the procession of the earth’s axis marked the North Star 12,00 years ago. Altair is the second brightest star in the triangle, and located in the constellation Aquila the Eagle, and is one of the closest stars to the earth at only 16 light years. Deneb is the third brightest star in the Triangle and the brightest star in Cygnus the Swan, and lies at a distant 1400 light years.


When you connect all three stars by an imaginary line, the asterism forms a large triangle in the night sky. The Summer Triangle is easy to spot in the summer but remains in the evening sky through fall.


During Fall the Summer Triangle is high overhead after the sunsets in early evening. A good way to spot the Summer Triangle this fall is to locate the bright planet Jupiter in the southeast. The Triangle lies above Jupiter and slightly to the west above you. The Triangle is large but the stars that form it are bright.