120520 Summer Triangle starscape
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click image to play 36s illustration
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ASTRO:
type=starscape; const=Aquila, Cygnus & Lyra IMAGE: Moon illumination=0% (new); exposure=DSLR OSC: 1x25s, f/3.5, ISO6400 EQUIPMENT: camera=Nikon D90 (stk); optics=NIKKOR 18-70mm DX kit zoom @ 18mm; filter=(none); mount=simple tripod; guider=(none) SOFTWARE: acquisition=(in-camera) processing=PhotoshopCC, RCAstro_GradXT & NoiseXT |
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The Summer Triangle is an astronomical asterism in the northern celestial hemisphere. The defining vertices of this imaginary triangle are at the stars Altair, Deneb, and Vega, each of which is the brightest star of its respective constellation, Aquila, Cygnus, and Lyra.
The formation's greatest declination is +45° and lowest is +9° meaning the three can be seen from all places in the Northern Hemisphere. From mid-to-tropical northern latitudes: the center of the triangle appears overhead around solar midnight during summer, and exactly so at about the 27th parallel north. This is when it crosses the sky completely by rising at sunset in the east and setting at sunrise in the west.
Both Altair and Vega are bluish white, rapidly rotating type A main sequence stars in the local neighborhood 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.
HISTORICAL RECOGNITIONS:
In lower northern latitudes and in March each year, the Summer Triangle first becomes visible in the early morning hours (just before sunrise), then progresses to full evening views beginning in July. It crosses the nighttime Meridian in mid-September, and then continues with shorter duration evening views through October. It then retreats into the dusk of evening sunsets in late-November and finally disappears below the western horizon in early-December, not to return until the early mornings of the following March.
The formation's greatest declination is +45° and lowest is +9° meaning the three can be seen from all places in the Northern Hemisphere. From mid-to-tropical northern latitudes: the center of the triangle appears overhead around solar midnight during summer, and exactly so at about the 27th parallel north. This is when it crosses the sky completely by rising at sunset in the east and setting at sunrise in the west.
Both Altair and Vega are bluish white, rapidly rotating type A main sequence stars in the local neighborhood 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.
HISTORICAL RECOGNITIONS:
- 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, and celebrated in the Qixi Festival. The stars also bear ceremonial significance in the related celebrations of Tanabata, Chilseok, and Thất Tịch, which were derived from Qixi.
- The asterism was remarked upon by Austrian astronomer Joseph Johann von Littrow, who described it in 1866 as the "Conspicuous Triangle" in the text of his atlas.
- Johann Elert Bode connected the stars in a map in a book in 1816, although he did not label it.
- 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 as Sommerliches Dreieck (Summerly Triangle) in 1934.
- The term was popularized by American author H. A. Rey and British astronomer Patrick Moore in the 1950s.
- 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".
In lower northern latitudes and in March each year, the Summer Triangle first becomes visible in the early morning hours (just before sunrise), then progresses to full evening views beginning in July. It crosses the nighttime Meridian in mid-September, and then continues with shorter duration evening views through October. It then retreats into the dusk of evening sunsets in late-November and finally disappears below the western horizon in early-December, not to return until the early mornings of the following March.