Hevelius Named Triangulum Minus Little Triangle Constellation in 1687

Summary: Johannes Hevelius introduced Triangulum Minus the Little Triangle constellation in 1687 as a smaller companion of existing constellation Triangulum.

Andromeda the Chained Maiden, with (lower right) Triangulum Majus and Triangulum Minus; Hevelius's depiction from perspective of outsider looking into celestial globe reverses actual east-west appearance of sky for Earth-based observer as insider looking outward at celestial globe; J. Hevelii, Firmamentum Sobiescianum (MDCXC [1690]), Fig. V: Public Domain, via ETH-Bibliothek e-rara

Seventeenth-century Polish astronomer Johannes Hevelius introduced Triangulum Minus the Little Triangle constellation in 1687 as a smaller companion for already existing triangular constellation Triangulum the Triangle.

Johannes Hevelius (Polish: Jan Heweliusz; Jan. 28, 1611-Jan. 28, 1687) introduced Triangulum Minus the Lesser Triangle constellation as one of 10 constellations that he had invented in Prodromus Astronomiae. The three-volume compendium consisted of the Prodromus; a star catalogue, Catalogus Stellarum Fixarum; and a star atlas, Firmamentum Sobiescianum sive Uranographia. Hevelius's death left the Prodromus Astronomiae unfinished and the catalogue and star atlas, which had been printed in 1687, unpublished. The astronomer-selenographer's wife, Polish astronomer Elisabeth Catherina Koopmann Hevelius (Polish: Elżbieta Koopman Heweliusz; Jan. 17, 1647–Dec. 22, 1693), finished the Prodromus and then published all three volumes in 1690 under the posthumous authorship of her husband.

Triangulum Minus appeared as the seventh of Hevelius's 10 newly created constellations in Chapter VIII, De Numero Aſteriſmorum & Stellarum, tum nonnullis Rebus animadverſione dignis, of section Tabulae Solares Novae ("New Solar Tables") in the Prodromus. The small triangle emerged from three new stars that he discovered in southeastern Triangulum the Triangle constellation. The new triangle's stars shone between Aries the Ram and Triangulum the Triangle, according to their discoverer.

"Triangulum Minus. Caeterùm; Triangulum minus, quod ex tribus novis Stellulis conſtat, etiam ex numero novorum meorum Siderum eſt; haud potuit ferè aliter denominari: cùm ſub altero Triangulo majori, & ſupra Caput Arietis ſplendeat," described Hevelius (page 117).

The forming of the new triangular constellation necessitated renaming the existing constellation. Hevelius retitled Triangulum as Triangulum Majus, as explained by English astronomy writer Ian Ridpath (born May 1, 1947) in his profile "Triangulum Minus the little triangle," included in Chapter Four: Obsolete Constellations of his Star Tales book (1988; revised and expanded, 2018) and posted on his eponymous website (www.ianridpath.com).

Aries the Ram, with Triangula pair (upper center), Majus and Minus, and Musca (Musca Borealis); Hevelius's depiction from perspective of outsider looking into celestial globe reverses actual east-west appearance of sky for Earth-based observer as insider looking outward at celestial globe; J. Hevelii, Firmamentum Sobiescianum (MDCXC [1690]), Fig. BB: Public Domain, via ETH-Bibliothek e-rara

Triangulum Minus neighbors with Aries the Ram and Triangulum Majus. The small celestial triangle brushes the Ram's northwestern borders and its constellatory parent's southeastern limits. A discarded constellation, Musca Borealis (Latin: "northern fly"), appears as an eastern neighbor, perched between northern Aries the Ram and southern Perseus the Hero, on two (Figures BB, W) of the three sky charts (BB, V, WW) on which Hevelius depicted Triangulum Minus.

The exclusion of Triangulum Minus from the list of 88 constellations approved in 1922 by the International Astronomical Union (IAU) rendered Hevelius's triangle obsolete. Its three starry components of 6 Trianguli (abbreviated 6 Tri; also known as ι Trianguli, Iota Trianguli, abbreviated ι Tri, Iota Tri), 10 Trianguli (10 Tri) and 12 Trianguli (12 Tri) were assigned to Triangulum the Triangle constellation.

Triangulum the Triangle, the constellation in which Triangulum Minus may be viewed as an asterism (Ancient Greek: ἀστερισμός, asterismós, “group of stars”), encompasses an area of 131.8 square degrees, which accounts for 0.320 percent of the sky, according to Ian Ridpath's table of constellations. Its area places Triangulum Minus as 78th in order of size among the 88 IAU-approved constellations.

Right ascension (abbreviated RA; symbol α) coordinates for Triangulum extend from 01 hours 31 minutes 27.9408 seconds to 02h 50m 39.9523s, according to the constellation boundary tables on the International Astronomical Union's website. In the equatorial coordinate system, right ascension identifies with terrestrial longitude.

Declination (abbreviated dec; symbol δ) coordinates for Triangulum stretch from plus 25.6050701 to plus 37.3470840. The equatorial coordinate system's declination associates with geographic latitude.

Constellation Triangulum offers full visibility to Earth-based observers occupying latitudes 90 degrees north and 52 degrees south. Partial visibility of the triangular constellation is available to stargazers stationed between latitudes 52 degrees south and 64 degrees south in the southern hemisphere (Ridpath, Constellations -- 2).

Triangulum the Triangle constellation numbers among 13 autumnal constellations listed by the American Association of Amateur Astronomers (AAAA) on The Constellation Home Page on the organization's website. Late autumn and early winter qualify for best viewing seasons of Triangulum the Triangle constellation in the northern hemisphere, according to science writer Kelly Kizer Whitt in "Triangulum the Triangle in northern skies," published Dec. 6, 2022, on the EarthSky website. December is the best month for observing Triangulum, according to James Miller in "Star Constellation Facts: Triangulum," posted July 15, 2016, on his website, Astronomy Trek.

Even though Hevelius's Triangulum Minus has been nullified as a constellation, the small triangle nevertheless remains as an asterism within its parent's territory. The Great Square of Pegasus the Winged Horse and Cassiopeia the Seated Queen function as finding aids for Triangulum, according to Kelly Kizer Whitt. Triangulum lies northeast of the Great Square of Pegasus and below distinctively w-shaped Cassiopeia. Triangulum Minus shines in southeastern Triangulum.

Perseus the Hero, with Triangula pair(lower center-right), Triangulum Majus and Triangulum Minus, and Musca (Musca Borelis); Hevelius's depiction from perspective of outsider looking into celestial globe reverses actual east-west appearance of sky for Earth-based observer as insider looking outward at celestial globe; J. Hevelii, Firmamentum Sobiescianum (MDCXC [1690]), Fig. W: Public Domain, via ETH-Bibliothek e-rara

Acknowledgment

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

Image credits:

Andromeda the Chained Maiden, with (lower right) Triangulum Majus and Triangulum Minus; Hevelius's depiction from perspective of outsider looking into celestial globe reverses actual east-west appearance of sky for Earth-based observer as insider looking outward at celestial globe; J. Hevelii, Firmamentum Sobiescianum (MDCXC [1690]), Fig. V: Public Domain, via ETH-Bibliothek e-rara @ https://www.e-rara.ch/zut/content/zoom/133931

Aries the Ram, with Triangula pair (upper center), Majus and Minus, and Musca (Musca Borealis); Hevelius's depiction from perspective of outsider looking into celestial globe reverses actual east-west appearance of sky for Earth-based observer as insider looking outward at celestial globe; J. Hevelii, Firmamentum Sobiescianum (MDCXC [1690]), Fig. BB: Public Domain, via ETH-Bibliothek e-rara @ https://www.e-rara.ch/zut/content/zoom/133931

Perseus the Hero, with Triangula pair(lower center-right), Triangulum Majus and Triangulum Minus, and Musca (Musca Borelis); Hevelius's depiction from perspective of outsider looking into celestial globe reverses actual east-west appearance of sky for Earth-based observer as insider looking outward at celestial globe; J. Hevelii, Firmamentum Sobiescianum (MDCXC [1690]), Fig. W: Public Domain, via ETH-Bibliothek e-rara @ https://www.e-rara.ch/zut/content/zoom/133921

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