"These are strange and breathless days,
the dog days, when people are led to do things they are sure to be sorry for after."
The Dog Days originally were the days when Sirius rose just before or at the same time as sunrise (heliacal rising), which is no longer true, owing to procession of the equinoxes.
The Old Farmer's Almanac lists the traditional period of the Dog Days as the 40 days beginning July 3rd and ending August 11th, coinciding with the ancient heliacal (at sunrise) rising of the Dog Star, Sirius. These are the days of the year with the least rainfall in the Northern Hemisphere.