WEST MICHIGAN — As temperatures peak over 90 degrees, shade and Lake Michigan water becomes a prized commodity. You’ll often hear people refer to the “dog days of summer" in these conditions, but where does this phrase come from—and what does it actually mean?
First, know it’s not about dogs panting in the heat, though that's often the modern image. Instead, the term has ancient roots, dating back to the civilizations of Greece and Rome. The “dog days” are tied to astronomy, specifically the star Sirius, the brightest star in the night sky.
Sirius is part of the constellation Canis Major, sitting about 50 trillion miles away from the sun! Canis Major translates from Latin to “Greater Dog.” In ancient times, the “dog days” referred to the period when Sirius appeared to rise in the sky just before or at the same time as the Sun each morning. This typically began in early July, lasting through mid-August. The Romans believed this celestial event brought with it extreme heat, drought, and even disease.
While Sirius shines brightly, its alignment with the Sun doesn’t actually influence temperatures. The heat we associate with this time of year is due to the Earth’s axial tilt and orbit around the Sun—not the presence of any particular star.
Sirius peaks in strength and perception behind the sun on July 23, and the dog days are often said to fall 20 days prior and 20 days later, between July 3 and August 11.
What does this mean for West Michigan's "dog days"? Our warmest average high is 83 degrees, lasting from June 29 to July 31, meaning our historical "dog days" are shifted slightly earlier, but still peaking mid-July.
Grand Rapids normally sees the most 90-degree days in July, with about 4. We have already recorded 5 such days in June, an indication we could see an above average July for heat!
So the next time someone grumbles about the “dog days,” you’ll know they’re invoking a bit of ancient stargazing lore—whether they realize it or not.
