What are the dog days of summer?

Have you ever wondered what the dog days of summer actually are?

Despite the name, they have nothing to do with dogs stretching out on a cool porch or refusing to go for a walk in the afternoon heat. The phrase actually comes from astronomy and one of the brightest stars you’ll ever see.

Once you know the story, you’ll never hear someone complain about the dog days of summer the same way again.

It all starts with one very bright star

So why are they called the dog days of summer?

The answer is Sirius, the brightest star in the night sky. Sirius is part of the constellation Canis Major, or the “Greater Dog,” which is why it’s often called the Dog Star.

Thousands of years ago, people noticed Sirius rising in the eastern sky around the hottest part of the year. That timing inspired a name that has survived for centuries.

But did people really think the star caused the heat?

Did ancient people blame the star?

In a way, yes.

Ancient Greeks and Romans believed Sirius added its heat to the Sun, making the hottest days of the year even hotter. Today we know that’s not true. Sirius is almost 9 light-years away, so it doesn’t affect Earth’s weather at all.

But they weren’t completely wrong about the timing.

Why does the hottest weather usually arrive after the longest day of the year?

Why isn’t the hottest day on the first day of summer?

It seems like it should be.

The summer solstice gives us the year’s longest daylight, but the land, lakes, and oceans continue storing more heat than they release for several weeks afterward. Think of leaving a cast-iron skillet on a warm stove. It doesn’t reach its hottest temperature the instant the burner is turned on.

Earth works much the same way, which is why the hottest stretch of summer usually arrives later.

So when are the dog days, exactly?

When are the dog days of summer?

There’s no official weather definition, but they’re commonly considered to run from July 3 through August 11. That’s the period traditionally associated with Sirius rising alongside the Sun.

Not every location experiences its hottest weather during those dates, but across much of the Northern Hemisphere, they’re often among the warmest weeks of the year.

The phrase has outlived the astronomy that inspired it.

Why do we still use the phrase today?

Because it paints a picture everyone understands.

Say “dog days of summer,” and most people immediately think of sticky afternoons, buzzing cicadas, afternoon thunderstorms, and air conditioners working overtime.

The science has changed since ancient times, but the expression still perfectly captures the feeling of midsummer.

A saying that’s thousands of years old

The next time someone mentions the dog days of summer, you’ll know they’re talking about much more than hot weather.

They’re unknowingly repeating a phrase inspired by ancient astronomers watching the brightest star in the night sky rise before dawn.

That’s a pretty remarkable story hiding inside an ordinary summer saying.

Nerdy Nugget

Sirius is about 25 times brighter than our Sun. It only appears as a tiny point because it’s nearly 9 light-years away, making it the brightest star we can see from Earth.

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