The Dog Days of Summer

What and When Are the Dog Days of Summer?

June 22, 2021

The “Dog Days” of summer last from July 3 to August 11. What are the Dog Days of summer, exactly? What do they have to do with dogs? The ancient origins of this common phrase might surprise you. Enjoy this article about the meaning behind the Dog Days of summer!

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

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.

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. Not including our own Sun, Sirius is the brightest star in the sky.

In ancient Greece, Egypt, and Rome, it was believed that the dawn rising of Sirius 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 Ancient Greek seírios, meaning “scorching.” 

For the ancient Egyptians, the dawn rising of Sirius (known to them as “Sothis”) also coincided 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. This is soon after the Summer Solstice in late June, which of course also indicates that the worst summer heat will soon set in.

Learn 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 with drought, disease, and discomfort.

Sirius was described as a “bringer of drought and plague to frail mortals, rises and saddens the sky with sinister light” by the Roman poet Virgil.

Is this just superstition? A 2009 Finnish study tested the traditional claim that the rate of infections is higher during the 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

Watch our video on the Dog Days and the Dog Star! Plus, try this Dog-Days Iced Tea to keep you refreshed in the heat.



Reader Comments

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Dog days

My mom always said that ordinary house flies will bite during dog days.

Dog days

My mom always said that ordinary house flies will bite during dog days.

Hatching Chickens during Dog Days

A friend claims that one should not hatch eggs during Dog Days. She claims that the chicks will be weak, sick, & not live through the winter. Any thoughts?

Dog days

For most of my childhood I have often been told that snakes bite more during dog days. My dad told us that the snakes eyes have a cloudy covering over them during the 'dog days'. Is there any scientific evidence of this ?

snake eyes

The Editors's picture

When snakes are about to shed their skin in summer, their eyes cloud over as the old eye covering layer is replaced with a new one. The eyes look milky in color and the snake’s vision is impaired until it sheds the old layer, usually a few days. This happens in summer, but not necessarily during the Dog Days.

Note, too that shedding can vary from species to species, as well as environmental conditions, the animal’s nutrition and their growth rate.

Dog days

Dog days of summer .. oh how i loathe thee.

My rooster not crowing and staying on perch

Weve had hard rains and very hot weather now my rooster is staying on perch not eating and not crowing. Do they do this during dog days

rooster troubles

The Editors's picture

Roosters and chickens can get heat stress, some signs being panting, lethargy, loss of appetite, holding their wings out. Make sure that your rooster has shelter/shade from the heat and plenty of water. Also check if he might be suffering from an illness. Hope this helps!


A bigger mystery to me is why August 17th is designated as the start of "Cat Days" in the almanac and always has been. What the heck are "cat days"?

Robins in July

On my walk around the track this morning I notice pairs of robins; one track the other, than flying very fast after the one it was stalking.
How can you tell the difference between a male and a female robin?

Cat Nights

“Cat Nights” harks back to a rather obscure old Irish legend concerning witches and the belief that a witch could turn herself into a cat eight times, but on the ninth time (August 17), she couldn’t regain her human form. This bit of folklore also gives us the saying, “A cat has nine lives.” Because August is a yowly time for cats, this may have prompted the speculation about witches on the prowl in the first place.