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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.
The English term was popularized by British astronomer Sir Patrick Moore in the 1950s, although he did not invent it. 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. "Northern Triangle" is a more neutral alternative.
South Sea Islanders called, and still call it, the "navigator's triangle". They use it to navigate on the open ocean in the Pacific, including reaching Hawaii. Commented on by one of the solar scientists during the NASA Edge Live Broadcast of the Transit of Venus, June 5, 2012. Satellite Kepler's mission to find and analyze planets around stars is being done on 100,000 stars in this navigator's triangle.
The stars of the Summer Triangle 
See also 
- Spring Triangle
- Autumn Triangle
- Winter Triangle
- Winter Hexagon
- Qi Xi
- Heavenly Market enclosure
- 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
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