The Dog Days of Summer 

I was playing Pokémon Go! the other day when I noticed that all the Pokémon around were all ones resembling dogs. I noticed the date and saw that it was close to the ecclesiastical solstice, and for the next couple days, there continued to be largely just dog Pokémon. I looked around and didn't find anything explicitly saying what the company that owned the game was doing, but I gathered that they were probably making a reference to the "Dog Days of Summer"! When I told Becca, she seemed familiar with the term—which a surprising amount of people seem to be—but didn't know where it came from. So, I thought I'd share it with everyone as well!

The "Dog Days of Summer" are often referred to as the hottest days of summer. On average, these days lay shortly after the summer solstice. The summer solstice marks the first day of the summer season. It is when the Earth has reached a point in its orbit where the Sun shines most prominently over the Northern Hemisphere of the Earth. To us—on Earth—this is the highest point the Sun appears to reach in our sky. Throughout the year—as we move around the Sun—how high the Sun appears on a given day changes. As we move from spring into summer—the Sun's highest point in the sky increases every day by just a bit until, at the solstice, the Sun reaches its highest point. Then, as summer goes on, the Sun's highest point gets lower and lower until we get to winter, where the Sun's highest point is at its lowest. Afterwards, the Sun will appear to rise higher every day as we march back toward Summer. This is where the word solstice comes from: sol=Sun, -stice=still. Solstice=sun-still. These are the points where the Sun stops appearing to get lower or higher in the sky and appears to change direction. This is also what causes our seasons. When the Sun is high above the Earth's northern hemisphere in the summer, more of its light is being converted into heat, causing the northern hemisphere to be warmer on average. Conversely, in the wintertime, far less of the Sun's light hits the northern hemisphere. So, the northern hemisphere becomes colder on average, giving us our winter. Now that we understand all of that let's talk about where the term "Dog Days of Summer" comes from.

It likely started with the Egyptians. The Egyptians were well-versed in math and astronomy. They paid close attention to how the sky appeared to change throughout the year and showed reverence for many parts and players in the sky. One particular object of interest that was extremely important to them was the brightest star in the sky: Sirius, the dog star, in Canis Major, the "big dog". But this star was not "Sirius" nor "the dog star" to them. To them, Sirius' name was Sopdet, their god of fertility and renewal. The days when Sirius/Sopdet rose just before the Sun in their sky matched up almost perfectly with the annual flooding of the Nile River. This is an INSANELY important period because when the Nile floods, it brings in fertile silt they used for agriculture. They believed Sopdet brought forth this annual flooding, which is why they associated her with agriculture and prosperity. Though—Sopdet is not depicted as a dog in Egyptian art and literature. So, it doesn't yet explain where the "dog days of summer" saying came from.

Egyptian Depiction of Sopdet

This association didn't occur until the Greeks came about and started interacting with the Egyptians. Through trade and eventual occupation—the Greeks' mythology and intellectual studies were influenced by the already long-established Egyptians. The Greeks were no doubt well aware of Sirius—they called it Seirios or "scorching"—it is the brightest star in the sky, after all. You'd be hard-pressed not to notice it if you often looked up. Combine this with the Greeks' observations of how the Egyptians held sacred this star with how they believed it affected the natural world—it should be no surprise that the Greeks would also believe Sirius affected their lives in some way. To the Greeks, though, Sirius did not herald flood and fertility. For the Greeks, when Sirius rose just before the Sun, it was a period of high temperature and drought. The Greeks believed that—because Sirius is so bright—Sirius' light, combined with the Sun, must be causing a tremendous amount of heat to bear down on them. The Greeks referred to this period as simply being the time that the star Sirius/Seirios was prominent—"the time of Seirios". It wasn't until later when the Romans came along and adopted/adapted much of Greek culture, that we finally came to the closest origin of the phrase. They called it: "dies caniculares" or "days of the dog star".

Today, we know that no star in our sky contributes any measurable amount of heat to our days. It's solely coincidental that the hottest days of the year occur when our brightest star and the Sun share the sky. But that isn't true for everywhere on Earth. Our upside-down friends in Australia are currently experiencing winter, despite Sirius sharing their sky with the Sun as well. But the phrase "Dog Days of Summer" lives on as a cute idiom for us northern hemisphere-ians.