It’s hot again, up in the Northern Hemisphere. It’s that time of year when the sun shines its most unforgiving beams, baking the ground and, indeed, us. It’s the portion of summer known as the hottest time of the year. Or, more delightfully, the dog days.
Contrary to common conjecture, the dog days do not take their peculiar name from weather that “isn’t fit for a dog,” or heat that is so extreme it drives dogs mad. These folk etymologies shrink in comparison with the actual background of the phrase, a story of astronomical proportions.
The dog days, in the most technical sense, refer to the one- to two-month interval in which a particularly bright star rises and sets with the sun, shining during the daylight hours and staying hidden at night. This star is known by three names: Sirius, the Dog Star, and Alpha Canis Majoris. Apart from being the most prominent star in the constellation Canis Major (Latin for “Greater Dog”), this heavenly body is responsible for the origin of the expression dog days, a phrase that has endured through millennia.
Classicists and astronomers will know the Dog Star as Sirius. The earliest record of this name comes from the Greek poet Hesiod, in Work and Days, written in seventh century BC. Meaning “searing” or “scorching,” Sirius encapsulates the Dog Star’s unusual brightness. Additionally, in Greek mythology Sirius is the name of the dog of Orion (a mythical hunter who has a constellation of his own adjacent to Canis Major), which further reinforces the Dog Star’s historical associations with canines. This tradition continues in the Harry Potter series; Sirius Black’s Animagus form is a large black dog.
The Dog Star’s connection to dogs was not only maintained by constellations and mythology, it was boosted by the fact that dogs seemed to take the brunt of the dog days. They suffered from the heat more intensely than humans seemed to, and were at greater risk of madness.
The English phrase dog days, which entered the language in the 1500s, is a direct translation from the Latin term caniculares dies, which refers to this specific seasonal phenomenon and is modeled after the same term in Hellenistic Greek. It is also from Latin that we got the word canicular, which refers to the Dog Star, as well the precursor to the expression dog days: canicular days.
The Dog Star, being the second brightest star that can be seen with the naked eye, did not escape the attention of ancient astronomers. Nor did its annual disappearance from the night sky and the corresponding influx of heat. Initially, ancient Greeks blamed the Dog Star for the sweltering weather, assuming that its brightness paired with the sun manifested in the hottest days of the year. This belief was debunked in the first-century BC by Greek astronomer Geminus, but the significance of the Dog Star remained untempered.
In ancient times, the dog days would have roughly corresponded to the summer solstice. Due to precession, however, the days have fallen later and later in the year. The exact dates of the dog days depend on your latitude, but by today’s estimation they begin on July 3 and come to a close on August 11.
Humans have been griping about the weather as far back as written history reaches, and the dog days were an important time for all. The Ancient Greeks and Romans, in particular, had grim feelings for Sirius, associating it with an outbreak of insufferable heat and fever. Civilization has long credited the objects in the sky with influence over the earth and its inhabitants; if it’s not the Dog Star cursing you with sultry summer heat and madness it’s the moon driving you to lunacy. It seems you can’t win when it comes to the celestial bodies.