Did you know there was a constellation called 'the triangle'? And that the ancient Hellenes were aware of it, too? Triangulum is a small constellation in the northern sky. It was one of the 48 constellations listed by the second century astronomer Ptolemy, and so named for its three brightest stars, which form a long and narrow triangle. The Ancient Hellenes called Triangulum 'Deltoton' (Δελτωτόν), after the upper-case letter delta (Δ). Hellenic astronomers such as Hipparchos and Ptolemy called it Trigonon (Τρίγωνον).

There is not a lot of mythology connected to this tiny constellation, but the lore that it has is quite important. Hyginus, in his 'Astronomica' explains the options:

"This constellation, which has three angles like the Greek letter Delta, is so named for that reason.
Mercury [Hermes] is thought to have placed it above the head of Aries, so that the dimness of Aries might be marked by its brightness, wherever it should be, and that it should form the first letter in the name of Jove [Zeus] (in Greek, Dis).
Some have said that it pictures the position of Egypt; others, that of Aethiopa and Egypt where the Nile marks their boundaries. Still others think that Sicily is pictured there.
Others, say that three angles were put there because the gods divided the universe into three parts." [II.19]

The latter is the only one that might need some explaining. Zeus, the greatest of the Olympian Gods, and the father of Gods and men, was a son of Kronos and Rhea, a brother of Poseidon, Hades, Hestia, Demeter, Hera. When Zeus and His brothers drew lots for the rule of the world, Poseidon obtained the sea, Hades the lower world, and Zeus the heavens and the upper regions, but the earth belonged to them all. To quote the 'Iliad' by Hómēros:

"Poseidon was very angry and said, "Great heavens! strong as Zeus may be, he has said more than he can do if he has threatened violence against me, who am of like honour with himself. We were three brothers whom Rhea bore to Kronos--Zeus, myself, and Hades who rules the world below. Heaven and earth were divided into three parts, and each of us was to have an equal share. When we cast lots, it fell to me to have my dwelling in the sea for evermore; Hades took the darkness of the realms under the earth, while air and sky and clouds were the portion that fell to Zeus; but earth and great Olympus are the common property of all." [XV.187]

The constellation Triangulum is visible at latitudes between +90° and −60°, and best visible at 21:00 (9 p.m.) during the month of December.