This week, a stifling heat wave is taking hold of millions of Americans from the Great Lakes into the Ohio Valley and New England.

True, it's July, and we expect hot temperatures; but as weather.com digital meteorologist Chris Dolce explains, this particular heat wave is, making for a very uncomfortable summer week.

Temperatures will finally give way when a the stifling regions by the end of the week.

Even once the heat wave abates, we'll still be left with typical sultry summer temps. In fact,the "dog days of summer" are just getting started.

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If you thought that was a term your grandma made up, you'll be surprised to learn the phrase dates back to ancient Rome. “Caniculares dies,” or days of the dogs, was what the Romans called the period from the first week of July to the second week of August.

Therefore, the dog days of summer only refer to the last part of the summer, not the whole season.

So that explains when and where the phrase comes from, but why dogs? The explanation is cool, especially if you like astronomy.

Sirius, aka the Dog Star

Sirius, the Dog Star

(NASA, ESA and G. Bacon (STScI))

You might have heard of a constellation named Orion. Often referred to as "The Hunter," Orion is a prominent constellation visible throughout the world. Nearby is the constellation Canis Major, which is Latin for "greater dog." According to constellation lore, Canis Major is one of Orion’s hunting dogs.

Located in Canis Major is a star named Sirius, also called the "Dog Star." With the exception of our sun, Sirius is the brightest star visible from Earth. The brilliant, blue-white star’s name comes from the Greek word for “searing.”

Because Sirius is so bright, it was easy to track even for early astronomers. During April and early May, Sirius was visible in the southwest after sunset. But by the time mid-summer would come along, Sirius would rise and fall with the sun and get lost in the daytime light.

However, the ancients knew that the "Dog Star" was still there, up in the sky with the sun during the hottest time of the year. They reasoned that since Sirius was so bright and up there with the sun, it must be adding to the heat to produce the hottest time of the year.

Does the 'Dog Star' Produce Heat?

According to Dr. Jon Nese, Penn State University professor, and former storm analyst for The Weather Channel, "Sirius is very luminous; if it suddenly replaced our sun, daylight on Earth would be about 25 times brighter than it is now."

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While Sirius may be bright, the effects of its energy do not affect Earth as much. "Sirius is also about half a million times farther away from our sun - something the ancients didn’t know."

So if the sun is a traditional lightbulb, Sirius is an LED light.

As it turns out, when the ancients blamed the "Dog Star" for boosting the heat during the summer, they were barking up the wrong tree.

MORE ON WEATHER.COM: Sultry Heat Wave Chokes Eastern U.S.

Kids cool off in the spray of an open hydrant on a hot evening in Lawrence, Mass. on July 16, 2013. (AP Photo/Elise Amendola)