Many assume the phrase “dog days of summer” stems from dogs lazing about on hot summer days, but that may not be the case. Instead, the origins of the term can be traced back to ancient Rome, according to the Old Farmer’s Almanac, a periodical reference book over topics including gardening, astronomy and folklore.
Ancient Romans called the hottest days of summer “diēs caniculārēs,” which means “dog days” because of the connection they saw between these hot, humid days and the star Sirius. Sirius, which is the brightest star seen from Earth aside from the sun, is known as the “Dog Star” because it is the brightest star in the constellation Canis Major, meaning “Greater Dog.”
Because Sirius is so bright, ancient Romans believed it exuded extra heat toward the Earth, causing the hotter temperatures in the summer. Sirius also rises and sets with the sun during the summer, so people began to see the sun and Sirius as a powerful duo of forces that teamed up to create the sweltering summer heat. It’s no wonder why Sirius means “scorching” in Greek.
Despite the Romans’ conjectures, these days are hottest not because of a star but because of Earth’s tilt, according to the Old Farmer’s Almanac. During the summer, Earth’s tilt causes the sun’s light to hit the Northern Hemisphere more directly and for a longer amount of time during the day, making the days both longer and hotter.
While the dates vary by location, The Old Farmer’s Almanac estimates the hottest period to stretch from July 3 to Aug. 11, so we are truly in the midst of the dog days of summer.