Canis Minor, the Lesser Dog, is a small constellation, one of Ptolemy's forty-eight, representing the second of Orion's two hunting hounds, set east of the greater dog near the edge of the Milky Way. It is dominated by the bright star Procyon, one of the nearest stars to the sun, whose name means before the dog, because it rises just ahead of Sirius, the Dog Star. With Sirius and Betelgeuse, Procyon forms the prominent Winter Triangle. In myth the two dogs accompany the hunter Orion across the sky. In astronomical tradition the constellation is a pattern of stars rather than a zodiac sign. These are the features of Canis Minor as the classical and modern traditions describe it, distinct from any astrological use of the region; despite its small size it holds one of the brightest and closest of stars.
The blank stretch of sky between Canis Minor, Orion and Hydra, left entirely unfigured by Ptolemy, was filled only in the early seventeenth century by Monoceros, the unicorn, one of several constellations introduced in this period specifically to give a name to faint stars that the ancient tradition had judged not worth marking. Procyon's closeness and brightness made it, like Sirius in the neighbouring Greater Dog, a useful marker of the seasons in several independent traditions, though it never carried the calendrical weight in Egypt that Sirius's heliacal rising did for the flooding of the Nile.