The constellation of Canis Major, the Great Dog, together with the constellation of Canis Minor, according to the Greek myth, are the dogs that follow the hunter Orion, a giant constellation in the winter sky.
Canis Major was one of the most important constellations in ancient times because of Sirius, the Dog Star (in the constellation it represented the nose of the dog), which is the brightest star in the night sky, from the end of summer to the whole of winter. However, Canis Major and Minor are not as famous as Orion, whose belt, made up of three stars, make it very easy to spot it in the sky at night.
Very often constellations are explained by one or more myths, mainly Greek or Roman.
As far as Orion is concerned, he was a famous hunter. According to one myth he boasted that no creature could kill him. The goddess Hera therefore sent a giant scorpion to kill him. Orion succeeded in killing the scorpion, but was poisoned and died, too. Both, Orion and the scorpion, were put in the sky, but in such a way that they would never meet again. Orion in fact can be seen during most of the winter, while the constellation of the scorpion only in summer. 🙂