The term the Dog Days of summer has roots in ancient Greece, and it refers to the months of July and August in the Northern Hemisphere. The star Siruis, also known as the Dog Star, is found in the constellation Canis Major (Orion the Hunter's faithful hunting dog). It is the brightest star in the sky, second only to the sun. It was believed that the appearance of Sirius in the sky at sunrise during July and August added to the heat of the day, hence the Dog Days were the hottest days of the year. :-)
