The mythical single-horned beast, the unicorn, is represented by this constellation which was unknown to the ancient Greeks. Monoceros was first depicted in 1612 under the name Monoceros Unicornis on a globe by the Dutch theologian and cartographer Petrus Plancius (this was the same globe on which Camelopardalis, another of his inventions, first appeared). Plancius apparently introduced the constellation because a unicorn appears several times in the Old Testament of the Bible.
Monoceros prances between Canis Major (below it) and Canis Minor (above) on the Atlas Coelestis of John Flamsteed (1729).
Monoceros fills a large area between Hydra and Orion where there was no Greek constellation. It is not prominent (its brightest stars are of fourth magnitude) but it lies in the Milky Way and contains a host of fascinating objects, most notably the Rosette Nebula, a wreath-shaped mass of glowing gas with embedded stars.
There are no legends associated with the constellation, as it is a modern figure, and none of its stars have names.
Chinese astronomers were adept at creating constellations from faint stars, but even they struggled in Monoceros. A chain of four stars consisting of 8, 13 and 17 Monocerotis plus one in southern Gemini formed Sidu, representing the four major rivers of China (Yangtze, Yellow, Huai and Si). Delta Monocerotis and one other star, probably 18 Mon, formed Queqiu, representing two hillocks either side of a gateway to the palace. According to Sun and Kistemaker (1997) Alpha Monocerotis was part of Tiangou, a guard dog, most of which lay in northern Puppis; other sources, though, place Tiangou farther south. Beta and Gamma Monocerotis seem not to have featured in any Chinese constellation.
© Ian Ridpath. All rights reserved