What’s a Dog Day and What does it have to do with the Star Sirius?

Ever wondered what people are talking about when they say the ‘Dog Days’ of summer? You might think it has to do with dogs in the summer. Well, you would not entirely be wrong! But surprisingly, the phrase ‘dog days of summer’ has more to do with the stars than to do with our furry companions.

When are the ‘dog days’ of summer?

The term ‘dog days’ traditionally refers to a period of particularly hot and humid weather during the summer months of July and August in the Northern Hemisphere. We often hear about the ‘dog days’ of summer, but not many know the origin. The most common theory is that the phrase is a reference to summer days so hot they aren’t even fit for a dog to be outside! But where does the phrase actually come from?

The dog days of summer are from July 3rd to August 11th of each year. They’re usually the hottest days of the year in the northern hemisphere, especially in the United States of America where the phrase is most popular. Even though the phrase has nothing to do with how hot it is for our fellow canines, the dog days of summer were known as the most unbearable days of the season back in the day until air conditioners came around.

But why is it called a ‘dog day’ if it has nothing to do with dogs?

The phrase ‘dog day’ is actually a reference to the star Sirius also known as the Dog Star. During the ‘dog days’ the Sun occupied the same region of the sky as the star Sirius which was the brightest star visible from any part of Earth. Sirius is part of the constellation Canis Major, or the Great Dog.

In the summer Sirius rises and sets with the Sun. Ancient Romans noticed this, along with the fact that the star itself appeared so bright during the same time the weather would become the hottest. Putting their observations together, they believed the star actually gave off heat and added to the Sun’s warmth, accounting for the long stretch of extremely hot weather! They started referring to this time as ‘diēs caniculārēs,’ or ‘dog days.’

In ancient Greece and Rome, these incredibly hot days were believed to be a time of distraught. The extreme heat often created real-life problems like drought or unrest in society, giving the ‘dog days’ the reputation of bringing bad luck and bad times that drove both dogs and men mad with heat! The Roman poet Virgil even wrote in the Aeneid about the star:

“Fiery Sirius, bringer of drought and plague to frail mortals,
rises and saddens the sky with sinister light.”

The name “Sirius” in fact, stems from the Ancient Greek word seírios, meaning “scorching.”

What else does history say about these peak summer days?

In ancient Egypt, people welcomed the arrival of Sirius, known to them as Sothis, in the sky. Every year as the Nile River would flood, usually beginning in late June, the floodwaters would bring in rich soil that was needed to grow crops in what was otherwise a desert. This event was called the Inundation. While no one in Egypt knew exactly when the flooding would start, they noticed a clue in the sky.

They observed that the Nile water started to rise when the star Sirius began rising in the sky before the Sun. Sothis and the Inundation were extremely important to the ancient Egyptians as their survival depended on the harvest that followed. Due to this, they began their new year with the new Moon following the appearance of Sothis on the eastern horizon.

Truth or superstition?

So now that we know why these hot days are often blamed on an unassuming star, let’s find out if there’s any truth to this! Even though Sirius is an extremely bright star, the extra heat felt on Earth has nothing to with any additional radiation from it.

Then why are these days so extra hot? The Earth’s rotation around the Sun and its own tilted axis is why we experience the seasons the way we do. The Sun is hotter in the Northern hemispheres during the summer months as the Sun’s rays hit the Earth in a more direct way due to the Earth’s tilt. For example, if the North Pole is tilted toward the Sun, it will be hotter in the Northern Hemisphere while if the South Pole is tilted toward the Sun, that means it’s winter in the Northern Hemisphere.

Are the Dog Days still relevant?

Since the ancient astronomers found a connection to Sirius, we have learnt a lot more about the Earth. We also know that stars shift and the Earth wobbles, so the ‘dog days’ of ancient Greece and Rome are not the same as the ‘dog days’ of now and they won’t be the same as the ‘dog days’ thousand years from now. These days the phrase simply refers to the peak period of summer.

Today, we know well that the appearance of Sirius in the sky has no actual effect on the seasons here on Earth. Although its appearance at the same time as the hottest period of summer has ensured that the lore of the ‘dog days’ continues on.

Did you enjoy reading this article? Would you like to know more about origin stories of interesting phrases and terms? Let us know what you think in the comments below!

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