Why Do We Say the “Dog Days of Summer”?

Dogs are man's best friend and adorable, but what do they have to do with summer?

Summer days

During the hot summer months in prior years, you’ve probably lounged by the pool or the beach with your pup while reading one of the best summer reads of all time. This year, while your summer plans may change due to COVID-19, the weather will still be hot. But what are the dog days of summer, and what do those days have to do with dogs? This is the real reason why dogs pant—and when you should start worrying.

“Sirius”-ly surprising origins

The phrase “dog days of summer” actually has nothing to do with man’s best friend. It turns out that the ancient Greeks and Romans weren’t referring to real dogs, but to the great astronomical one, Sirius. The “Dog Star” is located in the constellation Canis Major, known as the Greater Dog, and is the brightest star that shines at night. Think you know your constellations? See if you can spot all 14 iconic constellations in these pictures.

Sirius is also known as “Nile Star” or “Star of Isis” because ancient Egyptians noticed four thousand years ago that around the summer solstice, Sirius would appear to rise before dawn, which would be around the time when the Nile River would flood. Since ancient Egyptian life depended on agriculture, the flowing river would either bring great prosperity or great destruction. Here are 24 astronomy facts you never learned in school.

Why “dog days of summer”?

What does the star Sirius have to do with the “dog days of summer”? According to the Farmer’s Alamanac, during summer months and specifically on July 23rd, Sirius is extraordinarily bright and, in certain parts of the world, rises and sets with the sun at that time. Ancient Romans believed this shining star contributed to the sun’s heat, thus referring to this extremely hot period as diēs caniculārēs, or “dog days.” The term evolved to mean the 20 days before and after July 23rd, or July 3 to August 11, to coincide with Sirius aligning with the sun. However, depending on where you are in the world, the astronomical dog days and the rising of Sirius vary. Here are 31 facts you never knew about the summer solstice.

You could also find references to the “dog days of summer” in ancient texts. “If you go back even as far as Homer, The Iliad, it’s referring to Sirius as Orion’s dog rising, and it describes the star as being associated with war and disaster,” Jay B. Holberg, author of Sirius: Brightest Diamond in the Night Sky and senior research scientist at the University of Arizona Lunar & Planetary Laboratory tells National Geographic. “All throughout Greek and Roman literature, you found these things.” The phrase “dog days” has since taken on various meanings after its translation from Latin to English. Here are 18 Latin phrases that will make you sound smarter.

What does science have to do with it?

Even though Sirius is extremely bright, the extra heat is not because of any additional radiation from this star. The earth rotates around the sun and the Earth’s tilted axis is why we experience seasons. The sun is hotter in certain hemispheres because the sun’s rays hit the Earth in a more direct way due to Earth’s tilt. For example, if the North Pole is tilted toward the sun, that translates to hotter days in the Northern Hemisphere. Similarly, if the South Pole is tilted toward the sun, that means it’s winter in the Northern Hemisphere. However, stars shift, the earth wobbles, and the “dog days” of ancient Greece aren’t the same “dog days” of now, and the “dog days” of now won’t be the same as thousands of years from now.

How do you see Sirius?

To find Sirius in the night sky on winter evenings, locate the Orion constellation and then find Orion’s belt. Once you’ve located the three stars that make up Orion’s belt, move in a line down to the left until you find Sirius. Next, learn where a few more of your favorite animal-related sayings come from.

Madeline Wahl
Madeline Wahl is a Digital Associate Editor/Writer at RD.com. Previously, she worked for HuffPost and Golf Channel. Her writing has appeared on HuffPost, Red Magazine, McSweeney's, Pink Pangea, The Mighty, and Yahoo Lifestyle, among others. More of her work can be found on her website: www.madelinehwahl.com