What and When Are the Dog Days of Summer?

What Are the Dog Days of Summer?

The term “Dog Days” traditionally refers to a period of particularly hot and humid weather occurring during the summer months of July and August in the Northern Hemisphere.

Dog Days bright and clear
Indicate a happy year;
But when accompanied by rain,
For better times, our hopes are vain.

In ancient Greece and Rome, the Dog Days were believed to be a time of drought, bad luck, and unrest, when dogs and men alike would be driven mad by the extreme heat! Today, the phrase doesn’t conjure up such bad imagery. Instead, the Dog Days are associated purely with the time of summer’s peak temperatures and humidity.

Why Are They Called the “Dog Days” of Summer?

This period of sweltering weather coincides with the year’s heliacal (meaning “at sunrise”) rising of Sirius, the Dog Star. Sirius is part of the constellation Canis Majoris—the “Greater Dog”—which is where Sirius gets its canine nickname, as well as its official name, Alpha Canis Majoris. Sirius is the brightest star in the sky, not including our own Sun.

In ancient Greece, Egypt, and Rome, it was believed that Sirius’s dawn rising in mid- to late summer contributed to the extreme weather of the season. In other words, the “combined heat” of super-bright Sirius and our Sun was thought to be the cause of summer’s sweltering temperatures. The name “Sirius” even stems from the Ancient Greek seírios, meaning “scorching.” 

For the ancient Egyptians, Sirius’s dawn rising (known to them as Sothis) also coincided with the Nile River’s flood season. They used the star as a “watchdog” for that event.

Of course, the appearance of Sirius does not actually affect seasonal weather here on Earth, but its appearance during the hottest part of summer ensures that the lore surrounding the star lives on today!

When Are the Dog Days of Summer?

The exact dates of the Dog Days can vary from source to source, and because they are traditionally tied to the dawn rising of Sirius, they have changed over time. However, most sources agree that the Dog Days occur in mid- to late summer.

Here at the Old Farmer’s Almanac, we consider the Dog Days to be the 40 days beginning July 3 and ending August 11. These days occur soon after the summer solstice in late June, which also tends to be the beginning of the worst of summer’s heat.

More About Sirius

The Brightest Star in the Sky

Sirius is the brightest star in the sky if you don’t count our own Sun. Under the right conditions, it can even be seen with the naked eye during the day. Sirius is one star in a group of stars that form the constellation Canis Major, meaning “Greater Dog.” It’s no surprise, then, that the nickname of this big, bold star became “the Dog Star.” 

Given that Sirius is the brightest star in the sky, it’s not hard to find. Learn how to find the Dog Star in the night sky here.

The Dog Star in Ancient Egypt

In ancient Egypt, the Nile River flooded each year, usually beginning in late June. The people welcomed this event, called the Inundation, because the floodwaters brought rich soil needed to grow crops in what was otherwise a desert. 

No one in Egypt knew exactly when the flooding would start, but they noticed a coincidence that gave them a clue: The water began to rise on the days when Sirius (known to them as Sothis) began to rise before the Sun. Sothis and the Inundation became so important to the Egyptians’ survival that they began their new year with the new Moon that followed the star’s first appearance on the eastern horizon.

A Time of Ill Fortune?

Unlike the Egyptians, the ancient Greeks and Romans were not as pleased by Sirius’s appearance. For them, Sirius signaled a time when evil was brought to their lands in the form of drought, disease, or discomfort.

Virgil, the Roman poet, wrote in the Aeneid that “fiery Sirius, bringer of drought and plague to frail mortals, rises and saddens the sky with sinister light.”

Is this just superstition? A 2009 Finnish study tested the traditional claim that the rate of infections is higher during Dog Days. The authors wrote, “This study was conducted in order to challenge the myth that the rate of infections is higher during the dog days. To our surprise, the myth was found to be true.”

Dog Days of Summer Folklore

Old-timers believed that rainfall on the Dog Days was a bad omen, as foretold in this verse:
Dog Days bright and clear
Indicate a happy year;
But when accompanied by rain,
For better times, our hopes are vain.

“Dog Days are approaching; you must, therefore, make both hay and haste while the Sun shines, for when old Sirius takes command of the weather, he is such an unsteady, crazy dog, there is no dependence upon him.”
–The Old Farmer’s Almanac, 1817

Try this Dog-Days Iced Tea to keep you refreshed in the heat!