Spring Triangle Asterism Is an Asterism Within Great Diamond Asterism

Summary: The Spring Triangle asterism is an asterism within the Great Diamond asterism, formed by triangulating three of the celestial gem’s four stars.

Spring Triangle of Arcturus, Denebola and Spica (red lines), an asterism within the Great Diamond asterism, and alternative Spring Triangle of Arcturus, Regulus and Spica (green lines): Elop using Stellarium, CC BY SA 3.0 Unported, via Wikimedia Commons

The Northern Hemisphere’s Spring Triangle asterism is an asterism within the Great Diamond asterism, formed by reimagining three of the celestial gem’s four stars into a triangular pattern.

In astronomy, the term asterism (Ancient Greek: ἀστερισμός, asterismós, “group of stars”) designates a recognizable pattern of stars. The pattern may occur within the borders of one constellation, as, for example, the Cat’s Eyes asterism in the stinger at the tip of Scorpius the Scorpion’s curved tail. An asterism may also be constructed of stars from two or more constellations. The Great Diamond asterism exemplifies an intra-constellatory asterism, uniting four stars from four constellations.

The Spring Triangle displays in Northern Hemisphere skies March to May as a distinctive asterism. Spring’s triangular asterism also participates in a larger asterism, the Great Diamond.

The Spring Triangle associates three of the Great Diamond’s stars and constellations. The triangular asterism concerns the neighboring constellations of Bootes the Herdsman and Virgo the Virgin and draws in Virgo’s western neighbor, Leo the Lion. Bootes contributes Arcturus while Denebola lies in Leo and Spica hails from Virgo.

Spica rates as the Spring Triangle’s only resident of the Southern Celestial Hemisphere, the southern half of astronomy’s imaginary celestial sphere. The northward and southward stretches of Spica’s parent constellation across the celestial equator qualify Virgo as an equatorial constellation. Bluish-white Spica lies 11 degrees south of the celestial equator.

Arcturus and Denebola are both located in the Northern Celestial Hemisphere. Arcturus’ parent constellation, Bootes, maintains borders exclusively in the Northern Celestial Hemisphere. Orange-reddish Arcturus perches 19 degrees north of the celestial equator. Bluish-white Denebola is sited in east central Leo, 15 degrees north of the celestial equator. Constellation Leo, however, briefly straddles the celestial equator in fulfillment of the Lion’s claim as Virgo’s western neighbor.

Spica also rates as the Spring Triangle’s only binary. Its primary and secondary members maintain a close orbital period of every four days.

Denebola and Spica serve as closest stars to radiants (apparent points of origin) of spring meteor showers. The annual activity dates for the showers appearing to radiate from Leo and from Virgo overlap with the Spring Triangle’s prominent display in Northern Hemisphere skies.

The radiant for the Beta Leonids meteor shower approaches Denebola. The Beta Leonid activity dates annually span Feb. 14 to April 25 and peak around March 20, according to American amateur astronomer and meteor expert Gary W. Kronk. The Alpha Virginids meteor shower occurs annually between March 10 and May 6, with maximum activity April 7-18.

The Spring Triangle’s parent asterism, the Great Diamond, gathers together the neighboring constellations of Virgo the Virgin and Bootes the Herdsman and their respective western neighbors, Leo the Lion and Canes Venatici the Hunting Dogs. Coma Berenices the Hair of Berenice constellation separates Bootes from Leo and also intervenes between Canes Venatici and Virgo.

Virgo’s Spica, Bootes’ Arcturus, Canes Venatici’s Cor Caroli and Leo’s Denebola depict the Great Diamond. Spica and Cor Caroli define the Great Diamond’s southern and northern vertices, respectively. Arcturus and Denebola demarcate the Great Diamond asterism’s eastern and western vertices, respectively.

The version of the Spring Triangle comprising Arcturus, Denebola and Spica excludes Cor Caroli from participation by reducing the diamond asterism to a triangular asterism. The Great Diamond’s Spring Triangle geometrically traces a nearly equilateral triangle, with all three sides of nearly equal length.

Joe Rao, Space.com’s Skywatching columnist, credits George Lovi (Aug. 14, 1939-Feb. 18, 1993), Sky & Telescope's Rambling Through the Skies columnist, with naming the Spring Triangle, possibly as an analogy with the Summer Triangle of Altair, Deneb and Vega. He notes that Henry M. Neely (1877-1963), lecturer at New York’s Hayden Planetarium, knew the asterism within the Great Diamond as the Virgo Triangle.

An alternative version of the Spring Triangle, however, shuns Denebola for Leo the Lion constellation’s brightest star Regulus. Poised 11 degrees north of the celestial equator, the bluish-white star system lies along the ecliptic, the sun's apparent path across Earth's skies. The alternative asterism presents an acute triangle.

The takeaways for the Spring Triangle asterism that is an asterism within the Great Diamond asterism are that the Alpha Virginids and Beta Leonids appear to radiate from two Spring Triangle stars, that the triangular asterism rejects Cor Caroli for Denebola and that an alternative Spring Triangle asterism retains Arcturus and Spica but replaces Denebola with Leo’s brightest star, Regulus.

Spring Triangle comprises an asterism within the Great Diamond asterism and forms from the Great Diamond's three southernmost stars: Kate (Friendlystar at English Wikipedia), Public Domain, via Wikimedia Commons

Acknowledgment

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

Image credits:

Spring Triangle of Arcturus, Denebola and Spica (red lines), an asterism within the Great Diamond asterism, and alternative Spring Triangle of Arcturus, Regulus and Spica (green lines): Elop using Stellarium, CC BY SA 3.0 Unported, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Spring_Triangle_(Stellarium).png

Spring Triangle comprises an asterism within the Great Diamond asterism and forms from the Great Diamond's three southernmost stars: Kate (Friendlystar at English Wikipedia), Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Great_Diamond_map.gif

For further information:

Kaler, James B. (Jim). “Denebola (Beta Leonis).” University of Illinois Astronomy Department > Star of the Week.
Available @ http://stars.astro.illinois.edu/sow/denebola.html

Kronk, Gary W. "Alpha Virginids." Meteor Showers Online > Meteor Shower Calendar.
Available via Internet Archive Wayback Machine @ https://web.archive.org/web/20080516071922/http://meteorshowersonline.com/showers/alpha_virginids.html

Kronk, Gary W. "Beta Leonids." Meteor Showers Online > Meteor Shower Calendar.
Available via Internet Archive Wayback Machine @ https://web.archive.org/web/20080516071922/http://meteorshowersonline.com/showers/beta_leonids.html

Kronk, Gary W. Meteor Showers: An Annotated Catalog. Second Edition. The Patrick Moore Practical Astronomy Series. New York NY: Springer Science+Business Media, 2013.

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Available @ http://www.solstation.com/stars2/arcturus.htm

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Available @ http://www.solstation.com/stars2/denebola.htm

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Available @ https://earth-and-space-news.blogspot.com/2019/03/great-diamond-asterism-gathers-four.html

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Available @ https://earth-and-space-news.blogspot.com/2017/01/orions-belt-asterism-distinctively.html

Marriner, Derdriu. “Summer Triangle of Altair With Deneb and Vega Dramatizes Summer Nights.” Earth and Space News. Wednesday, Aug. 10, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/08/summer-triangle-of-altair-with-deneb.html

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Available @ https://earth-and-space-news.blogspot.com/2017/01/winter-hexagon-asterism-gathers-six.html

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Available @ https://www.space.com/2418-star-sight-celestial-diamond.html

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Available @ https://www.universeguide.com/meteorshower/alphavirginids

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Available @ https://www.universeguide.com/meteorshower/betaleonids