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What are the “Dog Days of Summer”—and when are they? The answer might surprise you. Enjoy this page about the meaning and origins of the “Dog Days of Summer.”


The Dog Days aren’t just when your dog starts panting on a sweltering summer day.

These days once coincided with the year’s heliacal (“at sunrise”) rising of the Dog Star, Sirius.  

Ancient folks thought that the “combined heat” of Sirius and the Sun caused midsummer’s swelter.

The rising of Sirius does not actually affect the weather, but for the ancient Egyptians, Sirius appeared just before the Nile River’s flood season. They used Sirius as a “watchdog” for that event.

Because it also coincided with a time of extreme heat, the connection with hot, sultry weather was made for all of time!


According to The Old Farmer’s Almanac, the Dog Days of summer are traditionally the 40 days beginning July 3 and ending August 11, which coincide with the dawn rising of Sirius, the Dog Star. This is soon after the Summer Solstice, which of course also indicates that the worst summer heat will soon set in.


The Old Farmer’s Almanac for Kids tells us all about the Dog Star, Sirius! Here are some of the most important facts:

Sirius is the brightest star in the sky, if you don’t count the Sun. Under the right conditions, it can even be seen with the naked eye during the day. Sirius is one star in a group of stars that form the constellation Canis Major, meaning “Greater Dog.” It’s no surprise, then, that the nickname of this big, bold star is Dog Star. Learn how to find the Dog Star in the night sky.

Sirius in Ancient Egypt

In ancient Egypt, the Nile River flooded each year, usually beginning in late June. The people welcomed this event, called the Inundation, because the floodwaters brought rich soil needed to grow crops in what was otherwise a desert. 

No one in Egypt knew exactly when the flooding would start, but they noticed a coincidence that gave them a clue: The water began to rise on the days when Sirius began to rise before the Sun. They called Sirius SOTHIS. SOTHIS and the Inundation became so important to the Egyptians’ survival that they began their new year with the new Moon that followed the star’s first appearance on the eastern horizon.


Unlike the Egyptians, the ancient Greeks and Romans were not pleased by Sirius’s appearance. For them, Sirius signaled a time when evil was brought to their lands with drought, disease, and discomfort.

Some people believed that the summer swelter was due to the combined heat from Sirius and the Sun. It makes sense that the name of the Dog Star, Sirius, means “scorching” in Greek.

Sirius was described as a “bringer of drought and plague to frail mortals, rises and saddens the sky with sinister light” by the Roman poet Virgil.

Is this just superstition? A 2009 Finnish study tested the traditional claim that the rate of infections is higher during the dog days. The authors wrote, “This study was conducted in order to challenge the myth that the rate of infections is higher during the dog days. To our surprise, the myth was found to be true.”

The Meaning of the Dog Star Today

Due to a very slow wobble of Earth’s axis, the Dog Star now seems to rise later than it did in ancient times. Its ascension no longer coincides with the start of the Nile flood (which does not occur anyway, because the river is now controlled by the Aswan Dam), but Sirius still makes its appearance during hot summer days. 


Old-timers believed that rainfall on the Dog Days was a bad omen, as foretold in this verse: Dog Days bright and clear Indicate a happy year; But when accompanied by rain, For better times, our hopes are vain.

Dog Days are approaching; you must, therefore, make both hay and haste while the Sun shines, for when old Sirius takes command of the weather, he is such an unsteady, crazy dog, there is no dependence upon him. –The Old Farmer’s Almanac, 1817

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