Dog Star

These are the dog days of summer in central Virginia. The weather is sultry: hot and very humid. As I write these words, the time is about 1:30 PM and the temperature has climbed to 95° with a heat index of 110°. Being outside means having your clothes get damp from perspiration in 5 minutes, even if you’re standing in the shade. One can picture a farmhouse with dogs lying on the ground under a front porch, or lying in the shade of a big tree in the front yard, panting from the heat.

But that halcyon scene is not the origin of the phrase Dog Days. The phrase comes from ancient Rome, when the bright star Sirius rose with the sun in summer months and became associated with the heat of the summer sun. (Sirius no longer rises with the summer sun due to precession of the equinoxes.) Sirius is the brightest star in the constellation Canis Major (Large Dog) and was called the “Dog Star.” Its official name was Canicula, “little dog.” The Dog Days of ancient Rome ran from July 24 through August 24. Traditionally, the Dog Days last 40 days. The Old Farmer’s Almanac lists the Dog Days as the 40 days beginning July 3 and ending August 11.

There is a tribe of people living in West Africa called the Dogon. They are believed to be of Egyptian descent and their astronomical lore goes back thousands of years to 3200 BC. According to their traditions, Sirius has a companion star that is invisible to the human eye. The Dogon say that this companion star orbits Sirius once every 50 years, is extremely heavy, and rotates on its axis. Two French anthropologists, Marcel Griaule and Germain Dieterlen, recorded this story which they heard from four Dogon priests in the 1930s.

That might have been the end of the story, except that in the 1970s astronomers discovered that Sirius has a companion star which orbits it once every 50.4 years. Astronomers named the companion star “Sirius B” and the “old” Sirius was renamed “Sirius A.” Sirius B was determined to be an extremely dense “white dwarf.” One teaspoon of matter from Sirius B would weigh 5 tons on Earth.

The Dogon say there is a third star (Sirius C) in orbit around Sirius A. Thus far, a third star has not been found. However, perturbations in the motions of Sirius A and B have led some astronomers to suspect there may be a third star.

How did the Dogon acquire their astronomical knowledge? They say it was given to them thousands of years ago by the Nommos, a race of beings living on a planet orbiting Sirius. According to the Dogon, the Nommos will return.

Frankly, I believe in coincidence. I believe in cross-cultural contamination of mythologies. But if one day astronomers do find a third star in the Sirius system, perhaps we should consider preparing some “Welcome Back” signs. Just in case.