Sky page: The origins of the 'dog days of summer'

As much of our nation swelters under the oppressive heat of August, pay close attention and I'll bet you hear someone refer to this time of year as the "dog days of summer." One might guess that the term comes from the seemingly lethargic behavior of our canine companions in the late-summer heat . . . but then one would be barking up the wrong tree.

No, its origin - like that of many everyday phrases - lies among the stars. The ancients, particularly those of the Mediterranean, knew late summer not only for its sweltering heat, but also for the disease and discomfort that accompanied it. It was a time when meat spoiled rapidly and food poisoning could take a toll on the population.

It was the ancient Romans and Greeks who noticed that Sirius, the Dog Star, rose with the sun (its "heliacal rising," as we know it today) during July - the hottest time of year. Many believed that the combined heat of the sun and Sirius in the daytime sky produced the scorching late summer heat - the "caniculares dies" - or "dog days" as the Romans called them. And, over time, the connection between the late summer heat and Sirius - and the phrase - became ingrained into culture.

Ideas such as this die hard; in fact, I'm sure some still believe it today. But it was the first-century BC Greek astronomer Geminus who explained it all. "It is generally believed that Sirius produces the heat of the Dog Days," he wrote, "but this is an error, for the star merely marks a season of the year when the Sun's heat is the greatest."

Nowadays, if you wish to watch the heliacal rising of Sirius, this month would be the time. In August, the Earth wobbles on its axis - an effect called precession - and over several millennia, the positions of celestial objects tend to shift slightly.

We can get some idea of what the ancients saw, however, by going outdoors during dawn on the week of Aug. 23 and facing southeast. There, low in the sky, you'll see the brilliant star Sirius sparkling and shimmering in a variety of colors.

With or without Sirius, late summer is hot. So enjoy the warmth while it lasts because it won't be long before we're complaining about the cold!