Sky Watch: The origin of summer 'dog days'

As much of Earth's Northern Hemisphere bakes in the heat of summertime, you'll hear someone refer to this time of year as the "dog days of summer."

Now one might guess that this 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 lies among the stars.

Early sky watchers kept close watch on the heavens in an attempt to correlate celestial and terrestrial activity and noticed that, during this hot season, the star Sirius rose around the same time as the sun, and the two moved across the daytime sky together.

Sirius -- the most luminous star in the night sky -- is known as the "Dog Star" because it marks the constellation Canis Major, the Great Dog. And many in olden times believed that it was the heat of Sirius, with that of the sun, that produced the scorching summertime temperatures -- the "caniculares dies" or "dog days" -- as the Romans called them. Over time, the link between late summer heat and Sirius -- and the phrase -- became ingrained into culture.

Sirius is a star much hotter than our sun but, at a distance of 53 trillion miles, the heat it provides us is negligible.

However, ideas such as this die hard; in fact, I wouldn't be surprised if some people still believe its connection today, despite it being debunked more than 20 centuries ago by the Greek astronomer Geminus:

daylight, we would now see those of winter -- including brilliant Sirius -- shining overhead at noon.