Why are the “dog days of summer” so named?
According to the Farmers’ Almanac, the phrase refers to the time period that the Sun occupies the same region of the sky as Sirius, the brightest star visible from any part of Earth and part of the constellation named Canis Major, which means “Greater Dog.”
“In the summer, Sirius rises and sets with the Sun. On July 23, specifically, it is in conjunction with the Sun, and because the star is so bright, the ancient Romans believed it actually gave off heat and added to the Sun’s warmth, accounting for the long stretch of sultry weather,” the almanac explains. The Romans referred to the 20 days before and 20 days after this alignment of Sirius with the Sun as “diēs caniculārēs,” or “dog days.”
The Farmers’ Almanac notes that this period is not the usually hottest stretch of summer because of any radiation from Sirius, but because of the Earth’s tilt. “During summer in the Northern Hemisphere, the tilt of the Earth causes the Sun’s rays to hit at a more direct angle, and for a longer period of time throughout the day. This means longer, hotter days,” it says.
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