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The Summer Triangle is an astronomical asterism involving an imaginary triangle drawn on the northern hemisphere's celestial sphere, with its defining vertices at Altair, Deneb, and Vega, the brightest stars in the three constellations of Aquila, Cygnus, and Lyra, respectively. In the mid to late 20th century, before INS, GPS and other electronic/mechanical equipment took their places in military aircraft, USAF navigators training at Mather AFB, Rancho Cordova, California referred to this asterism as the "Navigator's Triangle".
The term was popularized by American author H.A. Rey and British astronomer Sir Patrick Moore in the 1950s. The name can be found in constellation guidebooks as far back as 1913. The Austrian astronomer Oswald Thomas described these stars as "Grosses Dreieck" (Great Triangle) in the late 1920s and "Sommerliches Dreieck" (Summerly Triangle) in 1934. The asterism was remarked upon by J. J. Littrow, who described it as the "conspicuous triangle" in the text of his atlas (1866), and Bode connected the stars in a map in a book in 1816, although without label.
Near midnight the Summer Triangle lies virtually overhead at mid-northern latitudes during the summer months, but can also be seen during spring in the early morning to the East. In the autumn the summer triangle is visible in the evening to the West well until November. From the southern hemisphere it appears upside down and low in the sky during the winter months.
The stars of the Summer Triangle
- The Stars and Their Stories: A Book for Young People. published 1913.
- Summer Triangle at Basic Celestial Phenomena by Kerry Magruder
- Summer Triangle at The Astronomy Net
- Summer Triangle at DavidDarling.info
- Summer Triangle at Astronomy Picture of the Day
- Summer Triangle at Constellation Guide
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