Dog Days are defined as the period from July 3 through August 11 when the Dog Star, Sirius, rises in conjunction with the sun.
Everyone knows that the “dog days of summer” occur during the hottest and muggiest part of the season. But where does the term come from? Why do we call the hot, sultry days of summer dog days?
In ancient times, when the night sky was clear, different groups of people in different parts of the world drew images in the sky by “connecting the dots” of the stars. The images drawn were dependent upon the peoples culture. The Chinese saw different images than the Native Americans, who saw different pictures than the Europeans. These star pictures are now called constellations, and the constellations that are now mapped out in the sky come from our European ancestors.
They saw images of bears, (Ursa Major and Ursa Minor), twins, (Gemini), a bull, (Taurus), and others, including dogs, (Canis Major and Canis Minor).
The brightest of the stars in Canis Major (the big dog) is Sirius, which also happens to be the brightest star in the night sky. In fact, it is so bright that the ancient Romans thought that the earth received heat from it. Look for it in the southern sky (viewed from northern latitudes) during January.
In the summer Sirius, the “dog star,” rises and sets with the sun. During late July Sirius is in conjunction with the sun, and the ancients believed that its heat added to the heat of the sun, creating a stretch of hot and sultry weather. They named this period of time after the dog star.
Today, dog days occur during the period between July 3 and August 11. It is certainly the warmest period of the summer, but the heat is not due to the added radiation from a far-away star, regardless of its brightness. The heat of summer is a direct result of the earth's tilt.