Summer Triangle

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The Summer Triangle mapped on a star chart

The Summer Triangle is an astronomical asterism in the northern celestial hemisphere. The defining vertices of this imaginary triangle are at Altair, Deneb, and Vega, each of which is the brightest star of its constellation (Aquila, Cygnus, and Lyra, respectively).


The term was popularized by American author H. A. Rey and British astronomer Patrick Moore in the 1950s.[1] The name can be found in constellation guidebooks as far back as 1913.[2] 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 Joseph Johann von Littrow, who described it as the "conspicuous triangle" in the text of his atlas (1866), and Johann Elert 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 Cowherd and the Weaver Girl, a story dating back some 2,600 years, celebrated in the Qixi Festival. In the mid- to late-20th century, before inertial navigation systems and other electronic and mechanical equipment took their places in military aircraft, United States Air Force navigators referred to this asterism as the "Navigator's Triangle".[3]


The Summer Triangle in the context of the night sky, with dimmer stars fading out first and then fading in last

From mid-northern latitudes, the Summer Triangle appears virtually overhead around solar midnight during summer. It is also visible in the eastern sky in early mornings during spring. In autumn and winter evenings, the Triangle is visible in the western sky until January.

From mid-southern latitudes, the asterism appears inverted, with Deneb below Altair, and low in the sky during winter.[citation needed]

The stars of the Summer Triangle[edit]

Name Constellation Apparent magnitude Luminosity
(× solar)
Spectral type Distance
(light years)
Radius (solar radius)
Vega Lyra 0.03 52 A0 25 2.36 to 2.82
Deneb Cygnus 1.25 200,000 A2 3550 203 ± 17
Altair Aquila 0.77 10 A7 16.6 1.63 to 2.03

See also[edit]


  1. ^ Patrick Moore (20 October 1983). Patrick Moore's History of astronomy. Macdonald. ISBN 978-0-356-08607-1.
  2. ^ Alice Mary Matlock Griffiths (1913), The Stars and Their Stories: A Book for Young People.
  3. ^ Lt. Col. William E. Hubert, USAF (Ret.) (December 1, 2006). "Chapter Eleven: "Triple Rated" Copilot, (Ugh)!". Pilot Here Or Pile It There: A Memoir. AuthorHouse. p. 115. ISBN 978-142595689-9.

External links[edit]