Summer Triangle of Altair With Deneb and Vega Dramatizes Summer Nights

Summary: The Summer Triangle poaches Aquila's Altair, Cygnus's Deneb and Lyra's Vega to create an impossible-to-miss geometry in the night sky.

Milky Way and Summer Triangle: A.Fujii/NASA, Public Domain, via Wikimedia Commons

The Summer Triangle is an asterism, or recognizable pattern of stars, that particularly dramatizes summer nights in the Northern Hemisphere by poaching the brightest stars from three constellations in the northern sky.

The Summer Triangle consists of Altair in the constellation of Aquila the Eagle, Deneb in the constellation of Cygnus the Swan and Vega in the constellation of Lyra the Lyre. Cygnus is bordered by Lyra to the west. Aquila lies to the south of Cygnus’s dim yet distinctive southern constellationary neighbor, Sagitta the Arrow.

The widely spaced asterism logs extremes in light years. Altair’s light travels the least distance of the three stars. Altair lies 16.7 light years from Earth. At a distance of 25 light years, Vega is the next closest of the three.

Deneb claims fame as one of the most distant stars that is visible to the naked eye. The extremely luminous supergiant’s extreme distance has not yet been definitively calculated. Estimates range from 1,425 light years to 7,000 light years. Deneb’s light is estimated to take from one millennium (10 centuries) to one and one-half millennia (15 centuries) to reach Earth.

A special treat of the Summer Triangle’s noticeable prominence in summer months is the visible framing of the Milky Way between Vega and Altair. Deneb appears to lie in the middle of the Milky Way’s dim band.

The Summer Triangle’s visibility in the Northern Hemisphere is not restricted to its dramatic summer display. Early morning appearances occur in the eastern sky in spring. Autumn hosts evening views in the western sky.

While enjoying high visibility during the Northern Hemisphere’s summer, the Summer Triangle offers less dramatic viewing, with low placement, near the horizon, in Southern Hemisphere skies. The Summer Triangle appears oppositely, as an upside down version of the northern latitudes’ display, in the Southern Hemisphere. The Northern Hemisphere’s summer is the Southern Hemisphere’s winter.

The designation of Summer Triangle has an unclear, recent history. Joseph “Joe” Rao, an associate at New York’s Hayden Planetarium, finds that Hans Augusto “H.A.” Rey (Sept. 16, 1898-Aug. 26, 1977), who co-wrote the Curious George series with his wife Margret, may have been responsible for popular acceptance of the designation. Rey authored two constellatory books, The Stars: A New Way to See Them (1952) and Find the Constellations (1954), as attempts to simplify constellation identification. He referred to the Summer Triangle first in Find the Constellations and then, in 1962, updated The Stars with global sky charts that specifically noted the Summer Triangle.

On Saturday, Aug. 6, at around 10:30 p.m. Eastern Daylight Time, Vega reigns at the top of the Summer Triangle. From the viewer’s perspective, Altair marks the much lower right angle of the Summer Triangle while Deneb claims the asterism’s lower left angle.

Two hours later, after midnight, the apparent westward migration of stars across the sky causes Deneb to claim Vega’s spot as overhead star. In actuality, the westward drift is occasioned, not by starry movements, but by the Earth’s west-to-east rotation.

closeups of the individual stars composing the Summer Triangle: Deep Sky Colors -- Photography by RBA @DeepSkyColors, via Facebook June 25, 2015

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Summer Triangle: A. Fujii/NASA; triangle outline added by Cosmologie 101/French Wikipedia, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Wide-field_view_of_the_Summer_Triangle_modifié.jpg;
(without triangle), Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Dark_Rift_2012.jpg;
Francis Reddy, 2012: Shadow of the Dark Rift, Dec. 21, 2011, via NASA @ https://www.nasa.gov/universe/2012-shadow-of-the-dark-rift/

closeups of the individual stars composing the Summer Triangle: Deep Sky Colors -- Photography by RBA @DeepSkyColors, via Facebook June 25, 2015, @ https://www.facebook.com/DeepSkyColors/photos/a.511542708913047.1073741828.511507152249936/891106127623368/

For further information:

Deep Sky Colors - Photography by RBA @DeepSkyColors. "'Summer Vertices' During summer, in the Northern Hemisphere, away from city lights, is easy to see the three stars that form the 'Summer Triangle': Altair, Deneb, and Vega, the brightest stars in the Aquila, Cygnus, and Lyra constellations, respectively." Facebook. June 25, 2015.
Available @ https://www.facebook.com/DeepSkyColors/photos/a.511542708913047.1073741828.511507152249936/891106127623368/

Howell, Elizabeth. "Summer Triangle: Asterism of 3 Stars From 3 Constellations." Space.com > Science & Astronomy. Dec. 19, 2014.
Available @ http://www.space.com/28061-summer-triangle.html

Janne. "Linnunratapanoraama feat. Kesäkolmio." Flickr. Sept. 6, 2010.
Available @ https://www.flickr.com/photos/jannefoo/4963803403/

McClure, Bruce. “Come to know the Summer Triangle.” Earth Sky > Tonight. June 13, 2016.
Available @ http://earthsky.org/tonight/summer-triangle-predominates-during-the-summer-seaso

McClure, Bruce. “Summer Triangle on August evenings.” EarthSky > Tonight. Aug. 7, 2016.
Available @ http://earthsky.org/tonight/summer-triangle-high-overhead-at-mid-to-late-evening

Plait, Phil. "The Summer Triangle . . . Up Close." Slate > Blogs > Bad Astronomy. June 27, 2015.
Available @ http://www.slate.com/blogs/bad_astronomy/2015/06/27/vega_deneb_altair_up_close_and_personal.html

Rao, Joe. “Doorstep Astronomy: The Summer Triangle.” Space.com > Skywatching. June 17, 2005.
Available @ http://www.space.com/1206-doorstep-astronomy-summer-triangle.html

Rao, Joe. “See the Summer Triangle in Night Sky This Weekend.” Space.com > Skywatching. July 5, 2013.
Available @ http://www.space.com/21864-summer-triangle-weekend-night-sky.html

Rey, H.A. Find the Constellations. Boston MA: Houghton Mifflin, 1962.

Rey, Hans Augusto. The Stars: A New Way to See Them. Second edition. Boston MA: Houghton-Mifflin, 2008.

Rogelio Bernal Andreo. "Producing this image is something that occurred to me a few weeks ago when I was done shooting my target for the night but still had a few hours before twilight to do some quick shot of something." Facebook. June 25, 2015.
Available @ https://www.facebook.com/rbandreo/posts/866549040059773

Sessions, Larry. "Deneb is distant and very luminous." EarthSky > Brightest Stars. Aug. 19, 2015.
Available @ http://earthsky.org/brightest-stars/deneb-among-the-farthest-stars-to-be-seen

WPBT2 South Florida PBS. "Star Gazers - Sizing Up The Stars In The Summer Triangle." YouTube. July 18, 2013.
Available @ https://www.youtube.com/watch?v=-YyMvmCgl-U