for National Geographic News
The dog days of summer have arrived in the Northern Hemisphere. While they may make many us feel like we're swaddled in fur, the period is actually named after Sirius, the Dog Star.
Sirius rises with the sun when summer is at its hottest. The dog days traditionally run from July 3 to August 11.
The ancients believed extra heat generated by Sirius in conjunction with the sun caused this sizzling spell of weather. Sirius is the brightest star at night, after all.
But Sirius, which is found in the Canis Major (big dog) constellation, is some 50 trillion miles (80 trillion kilometers) from Earth—too far away to influence temperatures here.
In Roman times the dog days—or dies caniculares in Latin—were associated with intolerable heat, lethargy, disease, and, appropriately enough, mad dogs.
Pliny (A.D. 23-79), in his Natural History, refers to the increased risk of attack by rabid dogs in July and August. Bizarrely, he recommends feeding the animals large quantities of chicken droppings to prevent them from catching the disease.
In Britain The Husbandman's Practice, published in 1729, also offers survival tips for getting through the dog days. It suggests men should "abstain all this time from woman" and "take heed of feeding violently."
Ominously, the book warns, "The Heat of the Sun is so violent that Men's bodies at Midnight sweat as at Midday: and if they be hurt, they be more sick than at any other time, yea very near Dead."
Yet the ancient Egyptians, who experienced much hotter, drier summers, celebrated the return of the dog days, because they heralded a life-sustaining "miracle."
The start of the Egyptian sacred year was marked by the reappearance of Sirius. Soon afterward, the River Nile would flood, reviving parched farmland—despite a seasonal lack of rain. (The Egyptians weren't aware the water flowed from rain-drenched mountains in Ethiopia, more than a thousand miles [1,600 kilometers] to the south.)
Today Sirius appears several weeks later than in ancient times, because the stars and constellations gradually shift their position in relation to the sun.
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