The period from July 3 to August 11 is often called the "dog days of summer." For the origin of that term, we need to look to the stars.

Other than our own sun, the brightest star in the sky is Sirius, in the constellation Canis Major, the "Greater Dog." The ancient Egyptians called Sirius "the dog star." They knew that from early July to mid-August, Sirius rises and sets at about the same time as the sun. And since Sirius is such a bright star, they thought that its heat added to the heat of the sun, helping to create the heat waves that sometimes prevail in midsummer.

What the ancients didn’t know was that Sirius is more than half a million times farther from earth than the sun. So the intensity of the radiation that reaches earth from Sirius - and any other star for that matter - is negligible compared to what we get from the sun. So blaming the Dog Star for helping to bolster summer heat on earth is just, if you’ll pardon the pun, barking up the wrong tree.