Dog Days of Summer
We have officially entered the dog days of summer, which are traditionally considered to run from July 3 through August 11 each year.
Have you ever wondered where the phrase "the dog days of summer" comes from? Its origins date back to the ancient Greeks and Romans, who marked the changing seasons by observing the night sky. One of the brightest celestial objects they watched was Sirius, the "Dog Star," so named because it represents the nose of the constellation Canis Major, the Great Dog. Sirius is the brightest star visible in Earth's night sky.
In ancient times, around the middle to latter part of July, Sirius first became visible above the eastern horizon just before sunrise. This event, known as the heliacal rising of Sirius, coincided with the hottest stretch of the year. The Romans called this period dies caniculares—"the days of the Dog Star"—which eventually became the phrase we know today as the dog days of summer.
Traditionally, the dog days were defined as the 20 days before and the 20 days after the Sun's alignment with Sirius, an event that occurred around July 23 in Roman times. That places the traditional dog days between July 3 and August 11.
Of course, the ancient calendar doesn't perfectly match today's sky. Sirius returns to the same position relative to the Sun every 365¼ days, but over thousands of years Earth's slow axial precession has shifted the date of its heliacal rising. As a result, Sirius no longer appears just before sunrise in late July as it did in ancient Rome.
Today, observers in Rome, Athens, and even here in Indiana—all located between about 37° and 40° north latitude—see the heliacal rising of Sirius in mid-August. This year, Sirius will make its first pre-dawn appearance on August 12, nearly a month later than it did for the ancient Romans.
So while the calendar still tells us we are in the dog days of summer, the Dog Star itself is taking its time catching up.
