It's so hot you can fry a dog on the pavement... not that you'd want to.  However, that's not why they call it the "Dog Days."  The brightest star in the sky (if you don't count our sun, and why would you?) is Sirius, which is also known as the "Dog Star" because it is the most noticeable part of the constellation Canis Major, the Big Dog.  And, as we all know, Canis Major is Orion's hunting dog. (What are the Dog Days of Summer)

The heliacal rising of Sirius (meaning it rises in the morning) is visible in the Northern Hemisphere from July 3 to August 11, more or less, depending on where you actually are. (What are the Dog Days of Summer)  So, really, we could just as easily call it the Dog Days of July instead of the Dog Days of August... or whenever.  The further south you are, the earlier in the year Sirius rises... like in December.  (Little)  But here in the Northern Hemisphere, where everybody I know lives, Sirius rises in what happens to be the hottest part of the summer, at least, it was before global warming.  Why does it get so hot in the summer?  Well, that's easy!  It's a combination of our sun and Sirius.  No, I'm not being serious, but all those folks in the olden days believed that.  Of course, they believed all sorts of things that aren't true, but we can't blame them for trying.  (What are the Dog Days of Summer)

The Egyptians, not necessarily believing the nonsense about a distant star heating up our planet, associated Sirius with the Inundation, the annual flooding of the Nile, which brought life to that part of the world.  In fact, their new year began on the first full moon following the rise of Sirius.  On the other hand, the Greeks and the Romans, who notoriously believed in a lot of nonsense, saw the rise of Sirius as an ill omen, bringing famine and pestilence, and if anybody could do pestilence well, it was those guys.  Indeed, "Sirius" means "scorching" in Greek.  But then, disease rates really are higher in the summer. (What are the Dog Days of Summer)

If you want to locate Sirius, you'll first have to go outside at night.  It just won't work otherwise.  Then look up.  Next, find Orion's Belt – those three bright stars that almost everybody can identify, and then look down and to your left for the brightest star you can see.  Yup.  That's Sirius.  (Dog Days )  If you want somebody to blame for the heat, that's where to send your complaints. 

But, hey!  There's hope if you're patient enough, because of a little thingy called the Trepidation of the Equinoxes.  The earth, as it is wont to do, wobbles on its axis, so over time the stars shift in the night sky.  In just a scant 10,000 years Sirius will rise in the middle of winter.  Maybe then we'll call it the Dog Days of Winter, where it's so cold that even your dog wants to stay inside. (Dog Days)