Winter Hexagon Asterism Gathers Six Stars From Six Constellations

Summary: The Winter Hexagon asterism gathers six stars from six constellations for its prominent sky appearances from December to February.

asterism within an asterism: Winter Hexagon with Winter Triangle: Jim Thomas (Jomegat), Public Domain, via Wikimedia Commons

Also known as the Winter Circle or Winter Oval, the Northern Hemisphere's Winter Hexagon asterism gathers six stars from six constellations and also features an asterism within an asterism, the smaller Winter Triangle asterism, for its prominent sky appearances from December to February.

The six borrowed stars form a stellar hexagon that links them, outside of their individual constellations, in a recognizable pattern of stars known as an asterism. The six vertices, or angled meeting points of the imaginary hexagon’s six sides, are held by Auriga the Charioteer’s Capella, Taurus the Bull’s Aldebaran, Orion the Huntsman’s Rigel, Canis Major’s Sirius, Canis Minor’s Procyon and Gemini the Twins' Pollux.

In northern latitudes, the Winter Hexagon rises in the south. In December, the hexagonal asterism is high in the sky after midnight. Early January welcomes the Winter Hexagon’s highest point at around 11 p.m. In mid-February, the hexagon reaches its highest point around 8 or 9 p.m.

The Winter Hexagon is known as the Summer Hexagon or the Summer Circle in the Southern Hemisphere. English astronomer David Darling suggests extending the asterism southward, in the northern tropics and in the Southern Hemisphere, to include Canopus, the second brightest star in the southern constellation of Carina the Ship’s Keel.

Including Canopus, the second brightest star, after Sirius, in Earth’s night skies, would transform the Summer Hexagon into the Summer Heptagon, a seven-sided asterism. Amateur astronomer and Sky & Telescope contributor Bob King suggests a variant Winter/Summer Heptagon by adding Gemini’s Castor to the Winter Hexagon’s traditional sextet.

The Winter Hexagon asterism claims further structural interest for fueling the imaginations of stargazers. The hexagonal asterism contains another asterism within its asterismal boundaries by way of the Winter Triangle asterism. The Winter Triangle is an equilateral triangle that shares two vertices, Procyon and Sirius, with the Winter Hexagon. Orion’s Betelgeuse, located off-center inside the Winter Hexagon, tops the Winter Triangle.

High ranking brightness of all six stars explains the dramatic visibility of the Winter Hexagon asterism. All six appear in the list of 17 brightest stars in Earth’s night skies. Of those six, four (Sirius, Capella, Rigel, Procyon) are in the top eight.

Within the Northern Hemisphere’s brightest night stars, all six appear in the top 12 list. All except Pollux are in the top nine. The quartet of Sirius, Capella, Rigel and Procyon number in the Northern Hemisphere’s top six brightest night stars.

The Winter Hexagon is easy to locate because of its association with Orion. The Winter Hexagon encloses Orion and claims the constellation’s second brightest star, Rigel, as a hexagonal vertex. Rigel marks the constellation’s southwestern corner and the hexagon’s southwestern point.

The constellation of Greek mythology’s giant hunter dominates the sky as one of the night’s most conspicuous and most easily recognizable constellations. Orion’s brightest star, red supergiant Betelgeuse, marks the hunter’s right shoulder in front-facing depictions and his left shoulder in back-view illustrations. Rigel represents Orion’s left foot in front views and right foot in back views.

The Winter Hexagon is a showy asterism that shines on its own merits but also increases viewer interest with the dream catching possibilities of celestial bodies framed within the hexagon’s borders. Through its reliance upon Rigel, the Winter Hexagon always frames the recognizable magnificence of Orion the Hunter.

Apart from Orion’s constancy, other bright visitors also find themselves inside the Winter Hexagon. Amateur astronomer Bob King, known popularly as Astro Bob, noted the Winter Hexagon’s trapping of the waxing gibbous moon Saturday, Jan. 7, 2012, and Wednesday evening, Jan. 20, 2016. On Thursday, Jan. 9, 2014, Astro Bob shared Jupiter’s confinement within the Winter Hexagon.

The takeaway for the Winter Hexagon asterism is its wintry brightness as it brings together six bright stars from six familiar constellations for easy visibility from December to February.

Southern Hemisphere’s Summer Hexagon, visited by Jupiter; Winter Hexagon over Gensan, southern Philippines, Monday, Dec. 2, 2013, 22:27:28: peter jones (peterjonesdelacruz27), CC BY ND 2.0 Generic, via Flickr

Acknowledgment

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

Image credits:

Winter Hexagon with Winter Triangle: Jim Thomas (Jomegat), Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Wintersky.jpg

Southern Hemisphere’s Summer Hexagon, visited by Jupiter; Winter Hexagon over Gensan, southern Philippines, Monday, Dec. 2, 2013, 22:27:28: peter jones (peterjonesdelacruz27), CC BY ND 2.0, via Flickr @ https://www.flickr.com/photos/77526570@N02/11576097353/

For further information:

Astro Bob (Bob King). “Looking for Aurora Tonight? Check Out the Winter Hexagon + 2.” AreaVoices > Archives > January 2014. Jan. 9, 2014.
Available @ http://astrobob.areavoices.com/2014/01/09/looking-for-aurora-tonight-check-out-the-winter-hexagon-2/

Astro Bob (Bob King). “Moon and Winter Hexagon Bright on Bright Tonight.” AreaVoices > Archives > Jan. 7, 2012.
Available @ http://astrobob.areavoices.com/2012/01/07/moon-and-winter-hexagon-bright-on-bright-tonight/

Astro Bob (Bob King). “What Would It Look Like if Mars, Saturn or Neptune Replaced the Moon?” AreaVoices > Archives > February 2015.
Available @ http://astrobob.areavoices.com/2015/02/01/what-would-it-look-like-if-mars-saturn-or-neptune-replaced-the-moon/

Astro Bob (Bob King). “Wolf Moon Trapped by the Winter Hexagon.” AreaVoices > Archives > January 2016.
Available @ http://astrobob.areavoices.com/2016/01/19/wolf-moon-trapped-by-the-winter-hexagon/

Astro Bob (Bob King). “You Absolutely Must See the Winter Hexagon Tonight.” AreaVoices > Archives > January 2013.
Available @ http://astrobob.areavoices.com/2013/01/17/you-must-absolutely-see-the-winter-hexagon-tonight/

Constellation Guide Admin. “Winter Hexagon.” Constellation Guide. March 13, 2016.
Available @ http://www.constellation-guide.com/winter-hexagon/

Darling, David. “Winter Hexagon.” The Worlds of David Darling > Encyclopedia of Science.

Available @ http://www.daviddarling.info/encyclopedia/W/Winter_Hexagon.html

Hufnagel, Beth; Bob Stein. “16 Brightest Stars (Visible in the Northern Hemisphere).” Michigan State University Department of Physics and Astronomy > Courses > 1997 Spring.
Available @ https://www.pa.msu.edu/courses/1997spring/ISP205/sec-3/brightstars.html

McClure, Bruce. “Winter Circle: Brightest Winter Stars.” EarthSky> Favorite Star Patterns > Science Wire. Jan. 10, 2016.
Available @ http://earthsky.org/favorite-star-patterns/winter-circle-highlights-brightest-winter-stars

Millás, Isolina V. “The Brightest Stars of the Southern Hemisphere.” Popular Astronomy, vol. 26 (June-July 1918): 387-391.
Available via Harvard ADSABS (NASA Astrophysics Data System Abstracts) @ http://articles.adsabs.harvard.edu//full/1918PA.....26..387M/0000387.000.html

Ridpath, Ian. “The 25 Brightest Stars as Seen From Earth.” Ian Ridpath.
Available @ http://www.ianridpath.com/brightest.htm

Staal, Julius D.W. The New Patterns in the Sky: Myths and Legends of the Stars. Blacksburg VA: McDonald and Woodward Publishing Co., 1988.

“Winter Hexagon Over Stagecoach Colorado.” NASA’s Astronomy Picture of the Day (APOD).
Available @ http://apod.nasa.gov/apod/ap110103.html