By Professor Todd Brown / Contributor

Believe it or not, these cold January nights are the times that I remember the expression “the dog days of summer.” In central Illinois, the saying meant one thing: hot, humid and hazy summer days. But one of the possible origins of this expression relates to the winter constellation: Canis Major.

The ancient Greeks felt something had to explain the unusually hot weather that August would bring. Lacking the science of meteorology and themselves laying the foundation of astronomy and physics, they did not have many laws (and even fewer correct ones) to carve into granite. Since the sun made things hot then they reasoned that adding a smaller sun would make the weather even hotter. As late summer comes, a bright star starts to become visible just before sunrise. The star, Sirius, is not just bright, it is the brightest star visible after the sun. Residing in the constellation Canis Major, meaning the Big Dog, it should be no surprise that Sirius is also called the Dog Star. Lying next to Orion the Hunter, the Big Dog would have seen a lot of action in mythology (Orion: Fetch Cerebus, Canis Major! Stop chasing Pegasus! Bring me my golden sandals! Good boy!).

Its name leads to a plausible origin of the phrase. In August, the sun and Sirius are near each other in the sky and hence early people might believe this to lead to hotter days and nights. Move the calendar ahead by six months and, due to the earth’s travel through its orbit, the Sun and Sirius have moved to opposite sides of the sky all. Now the Dog Star rises just before sunset and rides fairly high in the sky during the winter nights. Would it be an inconvenient truth for Al Gore to look into the effect of Sirius on our weather?

No. As it turns out, Sirius is slightly larger than our sun and it is one of the closest stars to us but the sun is, by far, much closer. The sun lies eight light minutes away from us while Sirius is 8.7 light years. This means that light you see pouring from the sun took eight minutes to travel the gulf of space to reach earth. The light that shines on us tonight from Sirius left that star almost 9 years ago. With such a discrepancy in distance, the light that “beats down” on the earth from Sirius is over 10 billion times weaker than light from the sun. A candle’s warmth at arm’s length overwhelms the heat from Sirius or any star beyond the sun at their current distance.

So, Sirius the Dog Star might be the origin of the phrase regarding the dog days of summer but it is doubtful that it contributes to the heat. This is cast in even more doubt considering that the southern hemisphere is going through winter during our “dog days.” The Greeks took a shot at being able to explain the weather and they came up short. It would not be the last time we called the weather wrong nor would it be the last time that Sirius would throw humanity a curve.

Fast forward from the Greeks to the mid-1800s. By now, civilization had advanced to the point of the telegraph and early photography. People wore underwear, Mark Twain was alive and the Chicago Cubs were about to be founded. Scientists thought they knew a lot of stuff over those Greeks. Yet, by this time, a puzzle with the motion of Sirius was apparent.

All stars slowly drift with time as their paths through space are betrayed. Most went in a straight line but Sirius wandered through the sky much as a dizzy drunkard. The only explanation for this was that something was tugging on the star, and it had to be a large mass to make a star wander off-line. Finally, the telescopes of the mid 19th century showed the answer: Sirius had a very tiny, very dim companion. The bright star was renamed Sirius-A and the new dim star was called Sirius-B. By its influences on the bright Sirius-A, Sirius-B had to be very large (about as large as the sun).

It also shone with a bright-white light. This meant it was incredibly hot. For a massive star to be very hot but very dim could only mean one thing: it was very small. Puzzled but needing to categorize it, astronomers called it for what it was: white dwarf. Naming it was the easy part, now scientists had to explain how a sun-sized mass could be crammed into a ball the size of the earth.

It would take almost a century to pass before astronomers finally figured out how stars shown and evolved. Sirius-B was a star that initially was more massive than Sirius-A. In general, more massive stars age quicker by gobbling up their fuel reserves faster just as the high-power cars never advertise their MPG as a selling point because they are gas hogs. The weak star we see today had been a red giant eons ago until finally collapsing to the tiny remnant seen today.

Sirius-A still has us head scratching courtesy of the Greeks. Origin of the “Dog Days of Summer” phrase or not, Sirius-A has been the brightest star in our night skies since before recorded history. Babylonians, in 1000 B.C, referred to it in Cuneiform texts. The interesting point is that its color was described as red in accounts between 100 B.C. to 200 A.D. After that, including what you can see with your eyes today, it has shown with a brilliant white light. Were all the astronomers off during those three centuries or did Sirius undergo an unprecedented, and quick, change that we cannot explain today? It gives perspective and reason to leave a few blank pages at the end of our astronomy texts to be filled in at a later date. After thousands of years, we understand the stars better, our weather predictions have greater accuracy but there is still reason to stand outside on bone-chilling nights to gaze up and wonder how the book will end. Well, at least for a few moments before the hot tea is ready.

What else is out there this week: