The Dog Days of Summer

Posted by Kelly on July 29th, 2013

When Sirius joins the Sun in summer, the Dog Days are said to begin. Credit: NASA ESA G. Bacon (STScI)

When Sirius joins the Sun in summer, the Dog Days are said to begin. Credit: NASA ESA G. Bacon (STScI)

The “Dog Days of Summer” is a term used to refer to the hottest time of the hottest season. It may make you picture a dog lying in the shade and panting, but the original reference is from the Dog Star, Sirius.

For those who have a general idea of what stars are visible at what time of year, it may seem strange that the brightest star in the sky, Sirius, which brightens cold winter nights, is associated with summer. It’s not even visible for almost the entire summer. And therein lies the answer.

During summer, Sirius, the alpha star in the constellation Canis Major the Big Dog, lies near the Sun. The name Sirius means “scorching.” When Sirius disappears during the summer, it appears to join the Sun, and ancient Romans believed that the Dog Star added its warmth to that of the Sun’s as they neared one another, producing the hottest days of summer.

The Dog Days of Summer were traditionally referred to as July 3 to August 11. It was on these days that the Romans saw the Dog Star, Sirius, join the Sun at sunrise and disappear from the sky all night. However, because the Earth slowly wobbles on its axis, a phenomenon called precession*, the date for when Sirius joins the rising Sun in North America is now not until August 4. So the 40 days following August 4 would be the “new” Dog Days of Summer, ending on September 12.

*Precession alters the sky from what the ancients saw to what we see. Another example of this is with the ancient idea of astrology. For example, the ancients said that people born between July 23 and August 22 were under the Zodiac sign of Leo because that’s when the Sun would enter the constellation Leo. Only that is no longer true, for the Sun currently enters Leo on August 10 and leaves after September 15. This time shift is true for all signs of the Zodiac. Therefore, whatever Zodiac sign you thought you were born under is not correct. So if you weren’t suspect of the “science” of astrology before, you should be now. The next time you want to blame your good or bad luck on the alignments in the sky, remember what Shakespeare said: “The fault, dear Brutus, is not in our stars, but in ourselves.”

One person has commented

usha said,

i liked it and tanks for reminding what Shakespeare said.

Leave a Comment


Article Sections

Astronomy articles
Solar System Guide
Space Exploration
Cosmology articles
Book Reviews


Night Sky Guide
Buying a Telescope
Historical Eclipses
Meet Astronomers
The Constellations

Our Community

Read blog posts
Our newsletter
Meet the Team