The phrase “the dog days of summer” has been around as long as any of us have been alive. Did you know there are specific dates to which the phrase is referring? The reason for the name also has nothing to do with your panting, furry, four-legged, best friend. The name actually has to do with a specific constellation and star in the sky this time of year.

Where does the name “dog days of summer” come from?

The name “dog days” dates back to ancient times. It all ties in with a specific constellation and a specific star. The constellation is Canis Major and the particular star in question is called Sirius. Sirius is the brightest star in the sky (not including the Sun) and is most visible during the colder months of the year. However, during the summer, the star will rise in the pre-dawn sky in the same part of the sky as the Sun.

Canis Major
An illustration of the constellation Canis Major. The star Sirius would be the star that joins the triangle-shaped head of the “dog” with the body at the neck. Credit: Adobe Stock

The summer return of the star to the night sky is called a heliacal rising, meaning the first time the star becomes visible on the horizon in the eastern sky before sunrise. According to NASA, ancient Greeks believed the bright star Sirius enhanced the heat from the sun and was responsible for the hotter weather during that time of year. NASA says that the name Sirius means “the scorcher” in ancient Greek.

So why “dog days?” Sirius is part of the constellation Canis Major, which translates to “greater dog.” Ancient Greeks and Romans viewed the constellation as a large dog. Sirius, being the brightest star in the night sky and the most prominent in the constellation, is sometimes referred to as the “Dog Star.” Because the re-emergence of the so-called “dog star” came during the sweltering summer and in the same part of the sky as the Sun, ancient civilizations paid close attention to the star.

According to National Geographic, the phrase “dog days” was a translation from Latin to English that dates back to some 500 years ago. While the meaning behind the phrase became less well-known, the phrase stuck and continues to be used today when talking about hot, summer weather.

When are the “dog days of summer?”

At the current time, the dog days of summer begin in early July. The time frame for the “dog days” is a 40-day window, corresponding to the time when Sirius rises in conjunction with the Sun in the eastern sky. The official definition is the 20 days prior to and following the heliacal rise of the “Dog Star.” The currently used dates are a start on July 3rd and an end date of Aug. 11.

July conjunction of the Sun and Sirius
A NASA illustration of the July conjunction of the Sun and Sirius. The view is as seen from Earth in July showing the Sun’s position in the same part of the sky as Sirius. Credit: NASA/JPL-Caltech

Even though those are the given dates from many sources, it is unlikely you will see Sirius in the pre-dawn sky until after that window in the Youngstown area. The heliacal rise of Sirius at our latitude, around 41°N, won’t occur until somewhere between Aug. 10 and Aug. 20. Using a search tool on the website in-the-sky.org, the date Sirius first becomes viewable on the eastern horizon in the Youngstown area is Aug. 17. By definition, the timing of the “dog days” of summer in Youngstown would be the 20 days prior to and following that date. This means the Youngstown area’s “dog days of summer” would be July 28th – Sept. 6, assuming the calculator used has the correct first re-emergence of Sirius in the eastern sky for our area.

Will the “dog days” always happen in the summer?

The “dog days” will always be in the summer for anyone alive today and for several more millennia. but there will eventually be a shift in the season in which the “dog days” occur. Over time, the spin of the earth wobbles. This will eventually lead to changes in what stars are visible in the sky during different times of the year. That change is called precession and it takes place over a roughly 26,000-year cycle.

So eventually, in around 13,000 years, the heliacal rise of Sirius will occur in the winter months. With the definition of “dog days” being the 20 days prior to and following the first pre-dawn rise of Sirius on the eastern horizon, eventually the “dog days” will occur in the winter.

This doesn’t mean the summer heat will take place in the winter. Our calendar system, called the Gregorian calendar, is set up to keep the seasons at roughly the same exact time of year by adding a leap day every four years. Without that leap day, the occurrence of each season would also change over many thousands of years.