When things heat up around July and August, you’ll inevitably hear the phrase “dog days of summer.” No, this doesn’t have anything to do with canines lying around panting in the heat — instead, the phrase is a celestial reference. Sirius, the brightest star in the night sky, is nicknamed the “dog star” because it makes up the “eye” of the constellation Canis Major (Latin for “Greater Dog”). In Greek mythology, Canis Major is said to be a hunting dog who belongs to the legendary huntsman Orion. Cosmologically speaking, this relationship is fitting, because the three stars that make up the asterism Orion’s belt point to the “dog star” in the southern sky.
The phrase “dog days of summer” actually refers to a specific period on the calendar, from July 3 until August 11. The ancient Greeks and Romans believed these “dog days” occurred when Sirius appeared to rise with the sun, which always occurred during the summer. The idea was that the immense luminosity of Sirius along with the sun’s heat somehow created summer’s scorching temperatures. Of course, we now know this doesn’t make much sense. For one thing, Sirius is much farther away from Earth than the sun is — like 50 trillion miles farther — so the star has absolutely no effect on Earth’s climate. For another, the dog days of summer are relative to where you live on Earth, appearing earlier in the year for those living farther south and later for those in the north. Also, the position of Sirius is subject to Earth’s wobbly rotation — meaning that in 13,000 years, Sirius will instead rise in midwinter rather than midsummer. So no, “dog days of summer” isn’t an allusion to our cuddly canines, but a vestigial phrase derived from some 2,500-year-old astronomy.
Media Release/ InterestingFacts.com