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 puts the northern hemisphere closer to the sun. 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 vary by location, depending on latitude and climate.


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  1. I thought that today’s wonder was very “bright”. I think that it is interesting about how the ancient Romans came up with dog days. I did a report on Greek Mythology, and I found this cool website that is a lot like Google sky. I like the video, too. It’s cool how they show the dogs running around and around and around :)

    I think that tomorrow’s wonder is going to be about bookworms, or worms that live in the teacher’s apple.

    • Happy Friday, Meredith! You’ve done a LOT of reports on a LOT of interesting topics! We think it’s SO FUN to learn new things. We LOVE Google Sky! Once, we pointed it at the ground instead of the sky, and we’re pretty sure we were able to see the constellations and stars that folks on the opposite side of the globe were seeing at that time! It was really neat!

      By the way…CONGRATS! Because of your AWESOME post to our GHOST STORY Wonder yesterday, we’re sending you a kids’ SPOOKY STORIES book! Be sure to let you parents see this post or make sure they know we’re sending you this participation prize…and THANKS for being such a GREAT Wonder Friend! :-)

  2. I am so impressed with the connections Meredith as well as your learning continues to extend into the summer. Congrats also on getting a spooky story book I am sure you will be able to find several fun words in it to add to your writing.

  3. I think one of the statements here needs to be checked. It is not hotter because we are closer to the sun. That difference in distance is extremely small. The angle at which the suns rays are striking the earth are to blame for the heat.

  4. Thought you might be interested to know that the French word for a heatwave is “une canicule”, which stems from the Latin diēs caniculārēs. I was reading this wonder and thought that the phrase “diēs caniculārēs” looked somewhat familiar, and realised I’d learnt “une canicule” in French class as part of exam prep on the topic of the environment (Yes, I’m probably too old for this website).

    • Hi, Michelle! Thank you for teaching us something new today! You are NEVER to old to visit Wonderopolis! Wonder Friends come in all sizes, shapes and ages! We appreciate your comment and hope you’ll visit again soon! :-)

  5. I’m Jessica, and this website is so awesome! I learn something new from it every day I get on it! P.S. This is an awesome website! I WONDER what the next WONDER of the day is?!

    • Hello, Jessica! Thanks so much for leaving us such a WONDERful comment! We’re so glad to hear that you learn something new every time you visit Wonderopolis! :-)

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Have you ever wondered…

  • When are the dog days of summer?
  • What is the “Dog Star”?
  • Why are the dog days of summer so hot?

Wonder Gallery

dog resting in field_shutterstock_58184632Vimeo Video

Try It Out

Can you spot the constellations in the night sky? Use Google Sky to learn what to look for in the sky.

Print out a star map and then head outside tonight to try to find some constellations. Can you find Sirius, the Dog Star?

There’s nothing like cool treats to beat the heat when the dog days of summer arrive! Check out the fun and frosty recipes below and plan to enjoy some with your friends:


Still Wondering

Listen to ReadWriteThink’s Summer Adventures audio podcast to hear all about some great summer books to take along on your summertime adventures!


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