The Summer Triangle is an astronomical asterism in the northern celestial hemisphere. The defining vertices of this imaginary triangle are at

Altair Altair is the brightest star in the constellation of Aquila and the twelfth-brightest star in the night sky. It has the Bayer designation Alpha Aquilae, which is Latinised from α Aquilae and abbreviated Alpha Aql o ...

Deneb Deneb () is a first-magnitude star in the constellation of Cygnus, the swan. Deneb is one of the vertices of the asterism known as the Summer Triangle and the "head" of the Northern Cross. It is the brightest star in Cygnus and the ...

, and

Vega Vega is the brightest star in the northern constellation of Lyra. It has the Bayer designation α Lyrae, which is Latinised to Alpha Lyrae and abbreviated Alpha Lyr or α Lyr. This star is relatively close at only from the Sun, a ...

, each of which is the brightest star of its constellation ( Aquila, Cygnus, and

Lyra Lyra (; Latin for lyre, from Greek ''λύρα'') is a small constellation. It is one of the 48 listed by the 2nd century astronomer Ptolemy, and is one of the modern 88 constellations recognized by the International Astronomical Union. Lyra ...

, respectively). The greatest declination is +45° (rounded) and lowest is +9° (rounded) meaning the three can be seen from all places in the Northern Hemisphere and from the home of most of people resident in the Southern Hemisphere. The two stars in Aquila and Cygnus represent the head of an eagle and tail of a swan and these asterisms do not overlap, two small constellations intervening.

History

The term was popularized by American author H. A. Rey and British astronomer 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

Joseph Johann von Littrow Joseph Johann von Littrow (13 March 1781, Horšovský Týn (german: Bischofteinitz) – 30 November 1840, Vienna) was an Austrian astronomer. In 1837, he was ennobled with the title Joseph Johann Edler von Littrow. He was the father of Karl Ludwi ...

, who described it as the "conspicuous triangle" in the text of his atlas (1866), and

Johann Elert Bode Johann Elert Bode (; 19 January 1747 – 23 November 1826) was a German astronomer known for his reformulation and popularisation of the Titius–Bode law. Bode determined the orbit of Uranus and suggested the planet's name. Life and career ...

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 system An inertial navigation system (INS) is a navigation device that uses motion sensors ( accelerometers), rotation sensors ( gyroscopes) and a computer to continuously calculate by dead reckoning the position, the orientation, and the velocity ...

s and other electronic and mechanical equipment took their places in military aircraft,

United States Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Si ...

navigators referred to this asterism as the "Navigator's Triangle".

Visibility

From mid-to-tropical northern latitudes: *the centre of the triangle appears about overhead around solar midnight during summer, and exactly so at about the

27th parallel north The 27th parallel north is a circle of latitude that is 27 degrees north of the Earth's equatorial plane. It crosses Africa, Asia, the Pacific Ocean, North America and the Atlantic Ocean. At this latitude the sun is visible for 13 hours, 51 mi ...

. This means it at that time rises at sunset in the east and sets at sunrise in the west. *it is visible in the eastern sky in early mornings during

spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of water * Spring (mathematics), a geometric surface in the shape of a h ...

. *In autumn and winter evenings, it is visible in the western sky until January. From mid- southern latitudes, the asterism is in the north during the culmination season described above.

The stars of the Summer Triangle

Both Altair and Vega are bluish-white, rapidly-rotating A-type main sequence stars in the local neighbourhood of the sun. However, Deneb is a white supergiant star over 100 times as distant, and one of the most luminous stars in the entire galaxy.

Notes and references

;References ;Notes

History

Visibility

The stars of the Summer Triangle

See also

Notes and references

External links