Triangulum

Tri star chart (IAU and Sky & Telescope magazine, Roger Sinnott & Rick Fienberg).

One of the 88 IAU constellations. In Greek antiquity, it was called either Trigonon (triangle), or alternatively Deltoton (the letter Delta: Δ). The alternative name incorporates the religious connection for the ancients, but the constellation is missing on the Farnese Globe and the Mainz Globe.

Etymology and History

Origin of Constellation

The triangle constellation is ancient Greek. It did not exist in Mesopotamia; the stars probably belonged to the Babylonian constellation of the Hired Man, ^{mul lu₂}ḪUN.GA (Aries). Although it was consistently present as a separate constellation in Greece, the authors disagree about its meaning. Aratos calls it ‘the sign’; the mathematical astronomers call it ‘triangle’. Accordingly, Eratosthenes notes that some interpret it as the initial letter of the word ‘Dios’, i.e., as the Greek capital letter Δ (Delta). Dios is the genitive of the name of Zeus. The astronomer reports that when Hermes arranged the constellations in the sky, he inserted ‘of Zeus’ as a possessive inscription - i.e. ‘constellations of Zeus’, the highest god.

Alternatively, Eratosthenes, the librarian of Alexandria and teacher of the princes of Egypt, reported that the constellation was the Nile Delta. He says that the Nile created a triangular outline of Egypt. The constellation, therefore, symbolises the land that the Nile shapes.

The constellation is missing on the globe of the Atlas Farnese, but it is mentioned in all star catalogues: by Eudoxos, Hipparchus, Eratosthenes and Ptolemy. So, it was probably only omitted because it was too delicate or too tiny for the stonemason to fit between the ram and the princess. Interestingly, according to the Almagest, the triangle consists of four stars, with the fourth star located on one of the connecting lines. In contrast to the (equilateral) southern triangle, this classic triangle is very small and pointed: the fourth star, therefore, does not have to mark the baseline but is located on the smallest of the three edges.

In modern times, the constellation is called ‘the triangle’ by Johann E. Bode, for example. Whether he is referring to the small musical instrument remains a mystery, as the shape of the constellation is not changed. Mathematically, it makes no difference whether this geometry is called ‘three angles’ or ‘three corners’, so that the words tri-angel and drei-eck(en) are equivalent.

Greco-Roman

Eratosthenes

Var. 1 (περὶ τοῦ Δελτωτοῦ): This is the constellation above the head of Aries, and it is said that it is to compensate for its lack of brilliance is an easily recognisable letter, taken from the initial of the name of Zeus, and placed there by Hermes who organised the entire arrangement of the constellations. In fact, some say that Egypt derives its triangular shape from the triangle of the constellation, and that the Nile shape it has given to the contours of the country, not only guarantees its security, but also makes it easier to sow and provide a favourable climate for harvesting the fruits of the earth.

The Triangle has three stars, one on each of its angles, all three shining brightly.

Var. 2 (Δελτωτοῦ): This is the constellation above the head of Aries; it is said that the latter is quite dull, and that an easily recognisable letter is located above him, taken from the initial of the name of Zeus, and placed by Hermes who organised arrangement of the constellations. Some say that Egypt derives its triangular shape from the triangle of the constellation, and that the Nile, by this very shape it has given to the contours of the country, not only guarantees its security, but also makes it easier to sow easier and provide a favourable climate for harvesting the fruits of the earth.

The Triangle has three bright stars, one on each angle.

(Pamias and Zucker 2013)

Almagest Τρίγωνον

id	Greek (Heiberg 1898)	English (Toomer 1984)	ident.
	Τριγώνου ἀστερισμός	Constellation of Triangulum
1	ὁ ἐν τῇ κορουφῇ τοῦ Τριγώνου	The star in the apex of the triangle	alf Tri
2	τῶν ἐπὶ τῆς βάσεως 7 ὁ προηγούμενος.	The most advanced of the 3 on the basc	bet Tri
3	ὁ μέσος αὐτῶν.	The middle one of these	del Tri
4	ὁ ἑπόμενος τῶν τριῶν	The rearmost of the three	gam Tri
	ἀστέρες ὁ, ὥν ν’ μεγέθους ἢ, δ’ ἄ.

Transfer and Transformation of the Constellation

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  Perseus et Triangulum - Mercator 1551

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  Johannes Hevelius - Triangulum Majus, Triangulum Minus & Musca (also shows Aries, Andromeda, Piscis Boreus and Perseus)

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  Aries and Fleur-de-lis (Ignace Gaston Pardies-Plate 2)

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  Lilium, Triangulum - Corbinian Thomas

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  Sidney Hall - Urania's Mirror - Gloria Frederici, Andromeda, and Triangula

Mythology

Even Eratosthenes does not narrate any story or mythology.

IAU WGSN naming

1. The main star, α Trianguli, got a name in the earlies cycle of WGSN in 2016: The name "Mothallah" derives the term for "triangle" (al-muthallath) in Arabic and is, therefore, documented in Kunitzsch and Smart (2006).
2. It is proposed to name the second brightest term with the less known original Ancient Greek term "Deltoton".

References

• References (general)
• References (Babylonian)
• References (ancient Greco-Roman)
• References (medieval)