Triangulum

Triangulum is one of the smallest and plainest of Ptolemy's forty-eight, its handful of stars forming an elongated triangle with no bright star, no dramatic myth, and by its own article's account, only a passing ancient association with the Nile Delta or with Sicily. Its very plainness is what makes its onward history worth noting.

Al-Sufi's Book of Fixed Stars, the tenth-century Arabic reworking of Ptolemy's Almagest that reexamined and sometimes renamed the Greek constellations for an Islamic audience, preserved Triangulum among the northern figures essentially unchanged, neither renaming it after a different image the way Ursa Major became a funeral bier and Orion became a woman in the wider Arabic sky tradition, nor discarding it as too faint to bother with, the way several truly obscure ancient figures eventually were.

That quiet survival, geometry passed from Greek into Arabic astronomy with no reinterpretation attached, sits in deliberate contrast with the far more eventful passage other constellations made through the same Arabic tradition; Triangulum's shape offered so little to reinterpret, a plain elongated triangle rather than a scene with characters and action, that no culture inheriting it apparently felt moved to see anything else in it.

Its one genuine claim to modern fame, the Triangulum Galaxy tucked within its stars, was likewise found only once telescopes existed, never mentioned by any tradition that inherited the bare triangle before then.

Triangulum is a small northern constellation, one of the forty-eight listed by Ptolemy in the second century and retained among the modern eighty-eight. Its handful of stars form a narrow elongated triangle south of Andromeda, and the Greeks knew it as Deltoton for its resemblance to the letter delta; some ancient writers linked it to the Nile Delta or to the island of Sicily. Faint though it is, it contains the Triangulum Galaxy, a member of the Local Group visible in dark skies. In astrology the constellations of the sky are distinct from the zodiac signs that share some of their names, and a small figure such as Triangulum carries little of the symbolic weight the zodiacal constellations acquired. These are the features of the constellation as the classical and modern astronomical traditions describe it, separate from any astrological reading of the region.

Ptolemy's forty-eight is not the whole story of how the modern eighty-eight was assembled: the gaps between his figures, the faint, awkward spaces his hunters, animals and heroes left uncovered, were filled only later, by Johann Bayer in 1603, by Petrus Plancius and Jakob Bartsch in the early seventeenth century mapping the newly explored southern sky, by Johannes Hevelius in 1687, and by Nicolas-Louis de Lacaille in the 1750s, whose eighteenth-century southern constellations were named for instruments of the new science, telescope, microscope, furnace, rather than for any mythological figure. Triangulum's small neighbour, Triangulum Minor, was one of Hevelius's additions and did not survive into the standardised modern list, one of several constellations proposed after Ptolemy that later fell out of use entirely.