We often hear about the “dog days” of summer but few know what the expression means. Some say that it signifies hot sultry days “not fit for a dog;” others suggest it’s the weather in which dogs go mad. The Dog Days of Summer describes the most oppressive period of summer, between July 3rd and August 11th each year. But where did the term come from? And what does it have to do with dogs?
Why Are They Called the “Dog Days” of Summer?
The phrase is actually a reference to the fact that, during this time, the Sun occupies the same region of the sky as Sirius, the brightest star visible from any part of Earth and part of the constellation Canis Major, the Greater Dog. This is why Sirius is sometimes called the Dog Star.
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 Aug. 11.
Sun: It’s All About the Tilt
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 heat of summer is simply a direct result of the Earth’s tilt.
During summer in the Northern Hemisphere, the tilt of the Earth causes the Sun’s rays to hit at a more direct angle, and for a longer period of time throughout the day. This means longer, hotter days.
So what does it mean for you? Plan to take your beach vacation during this time and, of course, read our great ideas on ways to stay cool: