As the summer heat sizzles toward the end of July, you might hear someone refer to it as the “dog days of summer”. Most people think this phrase means that it is getting so hot outside that even the dogs feel miserable.

In reality, this ancient term refers to an astronomical occurrence that happens every year in July and the mythologies surrounding it.

In ancient times, various cultures believed the heat of summer was brought on by the early morning rising of Sirius in the eastern sky. Some thought it merged its heat with the sun to bring about drought, sudden thunderstorms, lethargy, and bad luck. In Egypt, Sirius predicted the annual flooding of the Nile and was worshipped as the goddess Sopdet.

Sirius shines brighter than any other star in the night sky and is only dimmer than Jupiter, Venus, the Moon, and the Sun. It is a binary star, meaning there is another star in orbit with it. As it moves through space, it gets closer and closer to our solar system, causing it to shine more brightly over the next 60,000 years.

Homer famously wrote about Sirius in his book Iliad:

“Priam saw him first, with his old man’s eyes, A single point of light on Troy’s dusty plain. 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 gleamed like this as he ran.”

Hesiod, the famous Greek poet, also wrote about Sirius:

“When the piercing power and sultry heat of the sun abate, and almighty Zeus sends the autumn rains, and men’s flesh comes to feel far easier,—for then the star Sirius passes over the heads of men, who are born to misery, only a little while by day and takes greater share of night—then, when it showers its leaves to the ground and stops sprouting, the wood you cut with your ax is least liable to worm.”

Culture after culture, century after century, Sirius continued to be blamed for the heat of summer. As astrology and superstition waned and more scientific methods were employed, humans understood that the rising of Sirius had no influence over the Earth’s weather or temperature. Although it continues to rise in the night sky every year in late summer, its shifting position will eventually have it rising in the middle of winter in about 10,000 years.