Beach vacations, the smell of sunscreen, and the sound of kids splashing in the pool mark the arrival of the so-called “dog days of summer.” While, to most of us, the well-known phrase evokes drowsy canines panting on a sweltering day, it has nothing to do with man’s best friend. Instead, “dog days” refers to an astronomical observation made more than 4,000 years ago of Sirius, a star 8.6 lightyears away from Earth.
The Celestial Origins of the “Dog Days”
In the ancient world, people followed the stars much like we mark the days of a calendar. Sirius, the brightest star in the night sky, came into position each year at the beginning of the hottest months in the Northern Hemisphere. Appearing just before dawn, the star was worshipped by the ancient Egyptians as the fertility goddess Sopdet. They called Sirius the “Star of Isis” or the “Nile Star” because its helical rising came at the time of the river’s annual summer flooding, which brought bountiful crops.
The ancient Greeks took Sirius’ presence a little more, well, literally. The bright star is part of the constellation Canis Major, which means “big dog” in Latin. The ancient Greeks nicknamed Sirius “dog star”; the name Sirius itself derives from the Greek word seírios, which means “scorching.” The star's annual appearance coincided with a time of year associated with extreme heat and, as described in Homer’s Iliad, a time of dangerous fever.
A bit later in the timeline, ancient Roman scribes like Seneca and Pliny posited that Sirius' early light contributed to the heat of the rising sun, and brought with it diēs caniculārēs, or “dog days,” which were blamed for everything from drought and vicious dog attacks to laziness and difficulty in concentration. They had a point: Who doesn't feel at least a little lazy and unfocused on the hottest days of the year?
The Dog Days Evolve
By the 1500s, “dog days” had made its way into the English vernacular, further enforcing the link between the phrase and the sensory effects of the season in the Western world. Published in 1564, The Hope of Health cautioned against performing medical procedures during summer’s “dogge daies” and 1729's British Husbandman’s Practice cautioned that rest and moderation were crucial during the heat of the day.
As the centuries progressed, the historic origins of the phrase became obscured, but “dog days” became a vivid, commonly understood descriptor of the hottest, often most unsettling days of the summer. The Old Farmer’s Almanac of 1817 warned that when “dog days are approaching; you must, therefore, make both hay and haste while the Sun shines, for when old Sirius takes command of the weather, he is such an unsteady, crazy dog, there is no dependence upon him.” In A Christmas Carol (1843), Charles Dickens used the phrase to describe the cold heart of Ebenezer Scrooge, who “carried his own low temperature always about him; he iced his office in the dog-days.” More recent popular culture has also made use of the phrase. Cases in point: Sidney Lumet’s Dog Day Afternoon, starring Al Pacino and based on an infamous bank robbery in the sticky summer of 1972, and Florence + the Machine's 2010 hit song “Dog Days are Over,” which, in part, was inspired by folkloric traditions of “waking up” after the languid summer season.
Just as its meaning has evolved, so too have the actual calendar dates associated with the dog days. The Egyptians marked it around June 25, the Greeks and Romans around July 19; by the 16th century, English liturgies marked canonical dog days from July 7 to September 5. During the British adoption of the Gregorian calendar in 1752, the dog days were shifted from July 30 through September 7. In modern times, they have moved from July 3 through August 11 — 20 days before and after the alignment of Sirius with the sun.
All this said, it is the Earth’s tilted axis, not Sirius, which brings the sweatiest months of July and August to the Northern Hemisphere. And depending on where you are latitudinally, the dog days can come at slightly different times: They happen earlier in the North and later in the South. The astronomical dog days — Sirius' time to shine — also appear at different times because the stars shift independent of a written calendar. As astronomers explain, the Earth wobbles as it spins and stars shift accordingly. Just as the dog days of thousands of years ago aren’t the same as today, about 13,000 years from now, Sirius will be rising in mid-winter, inviting entirely new meanings (“the flannel pajama-wearing, Netflix-binging dog days of winter”) to this ancient expression.