The “Dog Days” of summer are from July 3 to August 11 each year. They’re usually the hottest and most unbearable days of the season. We often hear about the “Dog Days” of summer, but few know where the expression originated. 

The phrase was first coined by the Romans, who noticed the hottest days of the year coincided with the star Sirus, the Dog Star, rising with the sun. During the “Dog Days” period, the Sun occupies the same region of the sky as Sirius, the brightest star visible from any part of Earth. Sirius is a part of the constellation Canis Major, the Greater Dog.

In the summer, Sirius rises and sets with the Sun. On July 23rd, specifically, it is in conjunction with the Sun, and because the star is so bright, the ancient Romans believed it actually gave off heat and added to the Sun’s warmth, accounting for the long stretch of sultry weather. They referred to this time as diēs caniculārēs, or “dog days.”

Thus, the term Dog Days of Summer came to mean the 20 days before and 20 days after this alignment of Sirius with the Sun—July 3 to August 11 each year.

While this period usually is the hottest stretch of summer, the heat is not due to any added radiation from Sirius, regardless of its brightness. The summer heat is simply a direct result of the Earth’s tilt in the Northern Hemisphere.

Enjoy the warm days, as winter is around the corner and predicted to be a chilly one.