(FOX19) - The dog days of summer is a common phrase often used when the weather feels oppressively hot outside. Many think the origin of this term has to do with the odd behavior of dogs (either lethargic or particularly animated) when the weather is hot. In reality, it has nothing to do with actual dogs, but a celestial dog.
The term dates back to ancient Greek and Roman times when early astronomers began studying the night sky. They noticed that it was around late July that the star Sirius returned to the night sky. Sirius is the brightest star and the most prominent star in the constellation Canis Major. As this constellation is said to resemble a dog, Sirius is often nicknamed the Dog Star.
The term "dog days" came to be known as the roughly 20 days before and 20 days after the return of Sirius to the night sky. The exact date of the return of Sirius varies based on your latitude, but occurs for most around July 20th.
There may be an explanation for how the term became associated with its current meaning though. Ancient Greeks and Romans noted that some of the most intense heat occurred during the dog days and thought that it may be due to the presence of Sirius and its light.
We now know that the stars we see in the night sky, even the brightest, are much too far away to have any impact on temperatures here on Earth. The association of the Dog Star with heat stuck though and thus the dog days of summer lives on in the English language.
Ironically, because the position of Sirius slowly changes in the night sky over time, it will eventually no longer rise in mid to late summer. In approximately 13,000 years, it will instead be rising in mid-winter. The dog days of summer will no longer exist and we'll instead have the dog days of winter.