Thursday, July 2, 2009

Stars signal the approach of summer

Stars signal the approach of summer
July 02, 2009

Staff Reporter

Believe it or not, the dog days of summer are almost officially here.

Sure, July has barely begun, and a soggy GTA is only now shaking off its first warm spell. But in the original Ancient Egyptian sense of the term, the dog days start July 3 and run through August 11. Like most everything else in Ancient Egypt, the term can be traced back to the whims of the gods.

"Early peoples were much more in tune with the sky and they tended to use it in useful ways," says John Percy, a professor of astronomy at the University of Toronto. "Certainly, the Ancient Egyptians were famous for keeping track of the rise of Sirius as a way of predicting when the Nile was going to flood."

Sirius, for the edification of earthbound Canadians, is the brightest star in the sky. It's also the eye in the constellation Canis Major, a giant celestial dog worshipped by the Ancient Egyptians. When, every summer, the star became visible at dawn, the Ancient Egyptians knew to brace themselves for major flooding - a seasonal phenomenon that often coincided with the warmest days of summer. And hence the expression, "dog days of summer," was born.

Their timing wasn't far off by Toronto standards. According to Environment Canada meteorologist Geoff Coulson, July is indeed the hottest month of the year, with an historical average temperature of 20.8 C at Pearson Airport. August comes in second, with an historical average of 19.9 C.

But not even the gods could foresee the "cold-low" currently hanging above the GTA.

"It's a low in the middle part of the atmosphere, not one that you'd normally see on the weather map the forecasters use on television," said Coulson. "It brings with it a dome of cool air that's sitting just above the ground."

As a result, today's high is about 6 C lower than normal, and rain is expected.

By this time next week, said Coulson, the cold-low will have dissipated and temperatures should be seasonal.

"We're showing a little bit of a bounceback as we go through the weekend," said Coulson. "What we're hinting at through the middle of the (next) workweek is sunshine and temperatures approaching where they should be this time of year."

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