Summer Triangle

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.

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. These are the same stars recognized in the Chinese legend of The Weaver Girl and the Cowherd, a story dating back some 2,600 years, celebrated in the Qixi Festival. In the mid- to late-20th century, before INS, GPS and other electronic/mechanical equipment took their places in military aircraft, United States Air Force navigators referred to this asterism as the "Navigator's Triangle".

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.

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