What are the "dog days of summer"?
Dog days are the hottest, most sultry days of summer season. In the northern hemisphere they usually fall between early July and September, whereas in the southern hemisphere it’s between January and early March. Of course the actual dates can vary greatly depending on the region, latitude and climate.
What does the “dog days of summer” name come from? In the Ancient Times, the people belived that Sirius (also called the Dog Star), in close proximity to the sun was responsible for the hot weather. The Romans referred to the dog days as diēs caniculārēs as the "Dog Star" is the brightest star in the constellation Canis Major (Large Dog). Sirius is also the brightest star in the night sky. The term "Dog Days" was also used earlier by the Greeks.
The Dog Days originally were the days when Sirius rose just before or at the same time as sunrise (heliacal rising), which is no longer true, owing to precession of the equinoxes. The Romans sacrificed a brown dog at the beginning of the Dog Days to appease the rage of Sirius, believing that the star was the cause of the hot, sultry weather.
Dog Days were believed to be an evil time when, according to Brady’s Clavis Calendarium from 1813, “the seas boiled, wine turned sour, Quinto raged in anger, dogs grew mad, and all creatures became languid, causing to man burning fevers, hysterics, and phrensies".
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Text source: wikipedia.org, image source: flickr.com