As Canis Major ascends the southern horizon, we enter the dog days of summer. But don’t fret, we have something for cat lovers too.
The “dog days of summer” are more than just something your grandparents say—they mark a historic and meteorological phenomenon representing the hottest and most humid stretch of the year, usually occurring from early July to early September in the northern temperate regions. But where does this evocative phrase come from, and what does it have to do with dogs?
The term traces back to the ancient Greeks, Romans, and Egyptians(1), who noticed that this sultry period roughly aligned with the heliacal (dawn) rising of Sirius, the brightest star in the night sky. Sirius is part of the constellation Canis Major, Latin for “Greater Dog,” which is why it’s often called the “Dog Star”. Ancient cultures believed Sirius’s simultaneous rise with the Sun compounded the season’s oppressive heat. In Roman times, the period became known as dies caniculares—the days of the dog star.(2)
Contrary to ancient belief, Sirius’s rising doesn’t actually intensify the summer heat. The real cause is the Earth’s tilt during summer, which directs the sun’s rays more directly onto the Northern Hemisphere, resulting in longer, hotter days. Nonetheless, the myth of Sirius adding to the summer’s heat has become part of the lore and provided lasting color to the phrase.
Today, dog days are a cue for summer rituals: relaxing by the water, seeking shade, and finding ways for both people and their furry companions to stay cool.
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“Canis Major – the Big Dog Constellation.“ Starwalk, (June 23, 2022). https://starwalk.space/en/news/canis-major-constellation-guide
“Canis Major.” Britannica Academic, Encyclopædia Britannica, 22 Oct. 2009. academic-eb-com.cobalt.champlain.edu/levels/collegiate/article/Canis-Major/476888.
“Dog days.” Britannica Academic, Encyclopædia Britannica, 20 Jul. 1998. academic-eb-com.cobalt.champlain.edu/levels/collegiate/article/dog-days/30786.”Sirius.” Britannica Academic, Encyclopædia Britannica, 10 Jun. 2024. academic-eb-com.cobalt.champlain.edu/levels/collegiate/article/Sirius/67991.