The Dog Days are known as the hottest days of the year in the Northern Hemisphere, and usually occur in July and early August. In ancient times, the sultry weather in Rome during these months often made people sick, which they blamed on the fact that this was when Sirius, the Dog Star, rose at about the same time as the sun. There are many different ways of calculating which days in any given year are the dog days, but it is impossible to be precise; nowadays it is generally assumed that they fall between July 3 and August 11—slightly later than they occurred in ancient times. Discuss
Source: The Free Dictionary