Triangulum

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

One of the 88 IAU constellations. In Greek antiquity, it was alternatively called Deltoton (the letter Delta).

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.

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.

References

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