When people mention “the dog days of Summer have arrived”, have you ever wondered what they mean?  Are they associating the behaviors of dogs laying in the shade, drinking more water, excessive panting, or taking more frequent naps during this time period of summer?

Unfortunately the expression has nothing to do with our actual furry companions or how they cope with the heat.

Sirius

There is one dog that is associated with the expression of  “dog days of summer”. From Latin, Sirius “the Dog Star”; one star of a binary star system, is the brightest star in our night sky from a distance of 8.6 light years away.  The dog star, Sirius A, is 20 times brighter than our sun. Sirius B, the companion star, is referred to as the pup and is a white dwarf. Sirius A is the only one that can be seen and is one of the stars that make up the Canis Major constellation.

Mythology

In Greek the star is called Seirios meaning “scorching” or “the scorcher”.  When the ancient Greeks noticed that approximately a 40 day period of extreme heat in the early summer coincided with the Sirius star rising and setting with the sun, they concluded that the additional heat was coming from the Sirius star.

The Greeks and the Romans were not pleased during this time of summer.  They believed that when the Sirius star made its timely appearance along with the Sun that it was going to be a time of evil brought to their lands in forms of droughts, disease, and discomfort.  Sirius was described by Roman poet Vigil as a “bringer of drought and plague to frail mortals, rises and saddens the sky with sinister light”.

A bust of Sopdet, Egyptian goddess of Sirius and the fertility of the Nile

Sothis

The ancient Egyptians referred to the star as Sothis and welcomed this event.  The Nile River flooded every year which brought rich fertile soil desperately needed to grow crops in the desert region.  At first they couldn’t tell exactly when this would occur but they eventually noticed that the floods would happen on the days when Sothis would rise before the Sun.

Sirius A and Sirius B.  “The pup” Sirius B is on the lower left.  The rings and spikes are instrumental effects

Fact or Myth?

The Dog Star has nothing to do with the extra heat during the summer.  The reason for the heat is due to the Earth being farthest from the sun in July.  During the summer , the Sun’s rays hit the Earth at a steep angle. The rays do not spread out as much which increases the amount of energy hitting any given spot on Earth.  The long daylight hours increases the time of the Earth to reach warmer temperatures. During winter time, the Earth is closer to the Sun causing the Sun rays to hit the planet at a shallow angle.  The rays are more spread out, which minimizes the amount of energy that hits any spot on Earth. The longer nights prevent the planet to reach high temperatures. This is of course if you’re dwelling somewhere on the Northern Hemisphere.

According to The Old Farmer’s Almanac, traditionally the 40 days of the Dog Days of Summer begin July 3rd and end on August 11th.  This time period however is not going to be accurate with our current calendar. Astronomer at the Adler Planetarium and director of the Doane Observatory, Larry Ciupik stated, “The calendar is fixed according to certain events, but the stars have shifted according to the way that the Earth wobbles…So in about 50 some years, the sky shifts about one degree.”  Meaning in several millennia from now, the Sirius star would be rising along with the sun during winter.

There is a small piece of truth behind the myth of the dog days that revolves around plagues.  A 2009 Finnish study tested the claim that the high rate of infections during this time period of summer.  The authors of the report who conducted the study confirmed this myth to be true.

References

Why is it hot in summer and cold in winter? (n.d.). Retrieved July 29, 2019, from https://www.loc.gov/rr/scitech/mysteries/seasons.html

Sirius (n.). (n.d.). Retrieved July 29, 2019, from https://www.etymonline.com/word/sirius

Constellation Guide. (n.d.). Retrieved July 29, 2019, from https://www.constellation-guide.com/constellation-list/canis-major-constellation/

Canis Major, the Great Dog. (n.d.). Retrieved July 29, 2019, from https://stardate.org/astro-guide/canis-major-great-dog

Kirkpatrick, N. (2019, May 23). The real meaning of the ‘dog days of summer’. Retrieved July 29, 2019, from https://www.mnn.com/earth-matters/climate-weather/stories/real-meaning-dog-days-summer

Klein, C. (2015, August 05). The Ancient Greek Origins of the ‘Dog Days of Summer’. Retrieved July 29, 2019, from https://www.history.com/news/why-are-they-called-the-dog-days-of-summer

Little, B. (2015, July 10). Why Do We Call Them the ‘Dog Days’ of Summer? Retrieved July 29, 2019, from https://news.nationalgeographic.com/2015/07/150710-dog-days-summer-sirius-star-astronomy-weather-language/

Old Farmer’s Almanac. (n.d.). The Dog Days of Summer. Retrieved July 29, 2019, from https://www.almanac.com/content/what-are-dog-days-summer