The phrase dog days of summer goes back to Roman times, and originally referred to weather patterns in the Mediterranean region. It references the rise of Sirius, the dog star. Dog days span roughly from July 23 to August 24, though no official dates exist. This 30 day period corresponds to the time when the Western Hemisphere sees the least rainfall.
It is easy to forget that we all live on a molten ball boiling and burning as it rotates around our little sun. But watch out, one 19th century commentator said that the dog days are the time where "the Sea boils, wine turns sour, dogs grow mad." I seem to remember Peter Mayle mentioning this quote in his book, A Year in Provence, but I can't be sure if my memory is correct..
This dog looks pretty cute though, she is behaving badly, putting her hands on the clean table cloth.