What are summer dog days?

If you live in the Northern Hemisphere, July and early August are the times when the weather is hot and the days are long. Often during this time, people will talk about the summer Dog Days.

Perhaps you have found that during this hot summer time, your dog becomes a bit more sluggish, or that they pant considerably more during their regular walks? Ok, they don't have anything to do with the word, really.

What are summer dog days? You need to remove your eyes off Fido and look up to explain why we say the Dog Days of Summer.