Mad dogs don’t give us our name for the hot, close days of July and August, though perhaps the prevalence of mad dogs at that time of year has kept the phrase dog days alive. The expression originated in Roman times as caniculares dies, days of the dog, and was an astronomical expression referring to the dog star Sirius or possibly Procyon. The Romans linked the rising of the Dog Star, the most brilliant star in the constellation Canis Major, with the sultry summer heat between July 3 and August 11, believing that the star added to the extreme heat of the sun. Canicular days, of course, have nothingto do with heat from the Dog Star, but the ancient expression remains popular after over twenty centuries.