How dog days of summer came to be


Sirius, the Dog Star, is deeply a part of our modern mythology. People still refer to the dog days of summer, but few know that they are referring to the brightest star in the nighttime sky.

In August, Sirius rises with the sun, a condition the astronomers call a heliacal rising. The ancient Greeks believed that the intense glow of the star added to the sun’s heat, leaving us with those nasty, late-summer “dog days.”

The word “Sirius” is our version of the Greek name “Seirios,” which means, loosely translated, the Scorching One or, even more loosely translated, Hot Stuff.

Hippocrates, the ancient Greek physician and the father of modern medicine, attributed illnesses like malaria to its hot, unholy summer glare. He was probably unaware that the hot summer sun also brought malarial mosquitoes.

He was perhaps thinking of a passage from Homer’s “Iliad,” an ancient poem that stood at the center of Greek culture. The “Iliad” describes the siege of the city-state Troy at the hands of Greek invaders.

As Troy’s King Priam stands on the fortifications of his proud city, he sees Achilles, the most formidable Greek warrior, charging toward the Trojan battlements. Homer compares the wrathful Achilles with the Dog Star:

“Sirius rises late in the dark, liquid sky on summer nights, star of stars, Orion’s dog they call it, brightest of all, but an evil portent, bringing heat and fevers to suffering humanity. Achilles’ bronze [armor] gleamed like this as he ran.”

The use of Sirius to predict a shift in climate goes back at least to the early Egyptian civilization centered on the Nile River.

Ancient Egyptians associated the star with the god Isis. They believed its rising caused the flooding of the Nile River, which deposited rich soil on the river’s banks.

In effect, Sirius made the crops grow. Since the star helped keep them alive, they worshiped it as a god and aligned many of their temples to its rising on the summer solstice.

The rising of Sirius with the sun was thus a dependable predictor of the life-giving Nile flooding.

It still is. If you’ve ever wondered why our forebears believed in the silliness of astrology, consider this:

If the floods come at the same time as the daytime rising of the stars, it’s human nature to assume that Sirius caused the rising. After all, the ancients had no other explanation and wouldn’t have one for three millennia.

Furthermore, we should excuse our forebears for their confusion about the dog days. After all, we still call those hot, humid days in August the dog days of summer. Every time you utter that phrase, you are collaborating with the misinformation originated by the ancients.

Moreover, the ancients had no sense of the sun’s proximity or the relative distance to Sirius. To them, Sirius was simply the brightest star in the heavens, and stars were simple points of light. The sun was a far larger flaming rock.

The reality is somewhat different. The sun is a rather mediocre star that heats the Earth because it’s so close to us, at about eight light minutes away. Sirius is more than a tad more distant at 8.6 light-years away.

Compare eight minutes of your life with 8.6 years, and you’ll understand what I mean. There’s no chance whatsoever that a star that distant could add to the sun’s heat.

However, even the facts can be deceiving. If we were magically to replace the sun with Sirius, we wouldn’t like the results. Sirius produces about 25 times the energy of the sun. Life on Earth would never have formed. Thus, unlike our sun, Sirius rises above mediocrity — but just barely.

Many nearby stars that are not nearly as bright produce much more energy than Sirius. Orion’s right shoulder, the reddish star Betelgeuse, delivers a whopping 126,000 times the energy of our sun.

Sirius isn’t particularly voluminous, either. Our sun is about one million miles wide. With a width of 1.4 million miles, Sirius wouldn’t make it to the orbit of Mercury if it replaced the sun.

Betelgeuse is big, you betcha. If we replaced the sun with Betelgeuse, the star would extend past the orbit of Mars. Earth would be deep-fried inside the star.

Consequently, Sirius is the brightest nighttime star, not because it is particularly large or energetic, but because of its proximity.

As stars like Sirius and Betelgeuse remind us, our sun’s mediocrity is a blessing in disguise.

If a star is above the horizon during daylight hours in summer, it’s bound to be visible at night during the winter.

Around 9 p.m., look to the south to find the three stars in a line that form the belt of Orion. Using the belt as a pointer, look down and to the left for Sirius, which will probably be flashing violently, changing color, and generally flickering like nobody’s business.

As I had to assure many callers to Perkins Observatory, the star’s weird behavior is not a sign of an alien spaceship bent on global domination.

Instead, the star’s light is caught and pushed around by Earthly atmospheric turbulence, which is most active close to the horizon. Twinkle, twinkle, little Dog Star.

Because of its brightness, Sirius has, since classical Roman times, set the standard for twinkling, or what astronomers call scintillation.

According to the first-century CE astronomical historian Pseudo-Eratosthenes, “stars similar to it (Sirius) are called sirii by astronomers because of the scintillation of their light.”

The Dog Star gets its name from the constellation it inhabits. Canis Major, the Big Dog, is the hunting hound of the mighty hunter, Orion.

Like any serious despoiler of animal life, the stellar hunter has an emergency backup dog, the constellation Canis Minor, Orion’s “Smaller Dog.”

Another Dog Star, called Procyon, is the main star of Canis Minor. The star’s name means “before the dog” because it and its constellation rise slightly ahead of Sirius.

To find the Smaller Dog, look for the two stars that form Orion’s shoulders. Use them as pointers to the left to find the two naked-eye stars representing Canis Minor. Procyon is the brighter one.

Like Sirius, Procyon rises with the sun in summer, and its heat was also said to cause the dog days.

Many ancient stories recount the exploits of the two dogs. Oddly, none of them dwell on their relationship with Orion. Some sources mention that both canines are the hunting dogs of Orion but don’t describe any canine exploits.

Instead, they explain the presence of the dogs as a kind of natural justice. Hyginus, a first-century BCE Greek poet, writes that Orion was rewarded with his faithful companions because he was a “zealous hunter.”

Pseudo-Eratosthenes suggests that Orion valued his dogs because they helped “to ward off wild animals.” When the gods changed Orion into a constellation after his death, the dogs were placed beside him so that he “would lack none of his belongings.”

Most often, constellational historians identify Sirius or Procyon as the canine companion of somebody else entirely — Icarius, best known as the father of alcoholic intoxication.

For simplicity’s sake, I’ll tell the Procyon version of the story.

In a rare fit of godly generosity, the god Dionysus taught Icarus to make wine.

In those ancient days, only the gods got plastered. Humans simply couldn’t handle their liquor.

The prohibitionists among us might argue that it’s still true, but never mind. There were strict penalties for revealing the secrets of the gods.

So Icarius made some wine. He wasn’t about to try the new drink on himself, so he asked some local shepherds to act as guinea pigs.

The unsuspecting shepherds thought that Icarus had poisoned them. They killed the poor winemaker on the spot in the world’s inaugural orgy of stupid, drunken violence.

Procyon came upon his dead master and did the Lassie thing. He ran to Icarius’s daughter and dragged her to the fallen Icarus by the hem.

Daughter and dog committed suicide at the sad sight, and (of course) Zeus put the dog in the sky to commemorate their love and their grief.

Once they sobered up and realized what they had done, the hung-over shepherds high-tailed it to the island of Ceos. But Procyon was to have his final revenge.

The intense heat of his rising that summer brought disease and starvation to Ceos. The Ceosians prayed to Zeus for relief.

The king of the gods answered with the Etesian winds, which cool the islands for 40 days every year after the daytime rising of the Dog Star.

The inhabitants of Ceos took no chances. To ensure the perpetual return of the winds, they made yearly sacrifices to Sirius and Procyon just before the August daytime rising of the stars.

The dog stars have always been symbols of the simple yet profound spirit of faithfulness and protection our canine companions provide us. We have always been afraid of the night, but as long as the stars still shine, we will never be alone in the dark.

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