'Dog days of summer' owes its namesake to the stars, not summer heat

The position of the stars was an intrinsic part of ancient Greek and Roman life, shaping religious beliefs, marking seasons and helping travelers navigate on long journeys.

The days between July 3 and Aug. 11, often referred to as the "dog days of summer," are some of the hottest in the Northern Hemisphere. Contrary to popular thought, the burden these days place upon our beloved, canine companions has nothing to do with the phrase's origin.

Instead, the term "dog days of summer" has deep historical roots dating back thousands of years and is actually intertwined with the movement of the stars.

The ancient Greeks and Romans are thought to have helped coin the phrase in reference to the star Sirius, or Dog Star, which appears to rise just before the sun in late July.

Orion's dog rising in the heavens not only marked hotter days, but the star also served as an omen that could bring fever and catastrophe, according to National Geographic.

The position of the stars overhead was an intrinsic part of ancient life, which shaped religious beliefs, marked seasons and even helped people navigate long journeys by land and sea.

Following stars to mark time was like following a calendar since the stars are virtually in the same spot in the sky at a given time of the solar year. Thousands of years ago, people learned that The Dog Star was in the same area of the sky as the sun during the hottest time of the year.

Sirius also served as an important marker for the ancient Egyptians nearly 5,000 years ago, according to Space.com.

Rising just before the sun around June 25 in ancient Egypt, the "Nile Star" marked the return of annual floodwaters overflowing the Nile River. Its appearance signified a time for irrigation and renewed fertility in the surrounding lands, according to the report.

While the movement of stars was an exceptional means of keeping track of time for ancient people, the accuracy of the "dog days" corresponding with summer heat does not hold true today based on a variety of factors.

Unlike today’s solar calendar, the ancient population marked a month’s time by the duration of a moon phase. The words "month" and "moon" have similar origins in language for this reason.

The lunar calendar has only about 355 days compared to the solar calendar's 365. This small difference means that the lunar month does not always align with the solar month.

Another reason Sirius' position in the sky does not correspond with the hottest days of the year for some people is because of their latitude, which will change when the astronomical "dog days" occur.

Even now, the "dog days" for the ancient Greeks no longer correspond to the ones of today because of the Earth's movement.

As the Earth spins, it wobbles like a top, which changes the position of the stars depending on which way it is wobbling. Every 26,000 years, the Earth completes one full cycle of precession. As a result, the Dog Star no longer comes into position at the same time of the solar year as it once did.

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