The Greater Dog. Sirius, the brightest star in this constellation and the entire sky, is often called the Dog Star. Orion's hunting dogs, Canis Major and Canis Minor, have no relation to Bootes' Hounds, Canes Venatici. Canis Major was cautiously watched by the Egyptians when visible. It was said that on the date Canis Major became visible the nile would flood the countryside. It was also believed that when Sirius is at a high point in the daytime sky it adds to the sun's heat. Thus the nickname for summer of the "Dog Days".