What is dog days

Whew! It's hot in Wonderopolis today. In fact, it feels like the dog days of summer have arrived. But what exactly does that mean?

Many people believe the phrase “dog days of summer" stems from the fact that dogs tend to be a bit on the lazy side during the hottest days of summer. Of course, who can blame them? With that much fur, dogs that exercise during the hot days of summer can overheat easily.

However, the phrase doesn't stem from lazy dogs lying around on hot and humid days. Instead, to find the answer, we only need to look to the summer sky.

The ancient Romans called the hottest, most humid days of summer “diēs caniculārēs" or “dog days." The name came about because they associated the hottest days of summer with the star Sirius. Sirius was known as the “Dog Star" because it was the brightest star in the constellation Canis Major (Large Dog). Sirius also happens to be the brightest star in the night sky.

Sirius is so bright that the ancient Romans thought it radiated extra heat toward Earth. During the summer, when Sirius rises and sets with the Sun, they thought Sirius added heat to the Sun's heat to cause hotter summer temperatures.

For the ancient Romans, the dog days of summer occurred from about July 24 to around August 24. Over time, though, the constellations have drifted somewhat. Today, The Old Farmer's Almanac lists the traditional timing of the dog days of summer as being July 3 until August 11.

Although the dog days of summer are usually the hottest, they don't have anything to do with either dogs or the star Sirius. Instead, the tilt of the Earth explains why these days tend to be the summer's hottest.

During summer in the Northern Hemisphere, the tilt of the Earth causes Sun's light to hit the Northern Hemisphere at a more direct angle, and for a longer period of time throughout the day. This means longer, hotter days during the summer.

This explains why the dog days of summer are from late January to early March in the Southern Hemisphere. The actual dates of the dog days of summer will vary by location, depending upon latitude and climate.

The “Dog Days” of summer are from July 3 to August 11 each year. They’re usually the hottest and most unbearable days of the season. We often hear about the “Dog Days” of summer, but few know where the expression originated. Some think it’s a reference to the hot, sultry days that are “not fit for a dog.” Others suggest it’s the time of year when the extreme heat drives dogs mad. But where does the term come from? And what does it have to do with dogs? You may be surprised to see is has to do with the stars! Read on.

The “Dog Days” Expression Explained

The phrase is a reference to Sirius, the Dog Star. During the “Dog Days” period, the Sun occupies the same region of the sky as Sirius, the brightest star visible from any part of Earth. Sirius is a part of the constellation Canis Major, the Greater Dog.

In the summer, Sirius rises and sets with the Sun. On July 23rd, 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. They referred to this time as diēs caniculārēs, or “dog days.”

Thus, the term Dog Days of Summer came to mean the 20 days before and 20 days after this alignment of Sirius with the Sun—July 3 to August 11 each year.

Summer heat is due to the Earth’s tilt

While this period usually is the hottest stretch of summer, the heat is not due to any added radiation from Sirius, regardless of its brightness. The heat of summer is simply a direct result 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.

What do the “Dog Days” of summer mean to you?

If you plan to take a vacation during this time, read some of our great ideas to stay cool:

Natural Ways To Keep Cool This Summer

Keep 15 Ways To Keep Your Pet Healthy and Hydrated in the Heat

6 Creative Ways To Keep Cool During Hot Summer Days

Cool Ways To Exercise Safely In Summer

What To Wear When The Temperature Soars

Thirsty? Drink This!

Can basil Seeds keep you cool?

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.

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 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 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.