Those Doggone Dog Days of Summer: Blame it on a Star

For most people, the dog days refer to the muggiest, hottest days of the year, when the weather makes people—and animals—feel sluggish and worn out. Memes showing dogs melting in the heat tie canines to the sultry weather. But the term isn’t really actually about the hottest days, whenever they may occur. Nor does it refer to what the heat does to our canine companions. It is about specific days and, according to the calendar, the dog days of summer are drawing to a close.

The dog days of summer refers to the 40 days that begin on July 3^rd and end on August 11^th. According to The Old Farmer's Almanac, this timeframe marks the 20 days before the Sun and the star Sirius align with each other, and the 20 days after. During these 40 days, Sirius is too close to the Sun to be visible.

With a magnitude of −1.46, Sirius is easily the brightest star in the night sky. Its name comes from the Greek word Σείριος which means ‘glowing' or 'scorching'. It is almost twice as bright as Canopus, the second brightest star. For us, only our Sun shines brighter. Much of our perceived brightness, however, comes more from proximity than from actual luminosity. Our sun, of course, is very close to us, and Sirius is a close neighbor, only 8.6 light years away. Sirius A is about twice as massive as the Sun and about 25 times as luminous, but Canopus, Betelgeuse, and Rigel are all more luminous than it is.

Sirius isn’t actually a single star, but a binary star. The larger of its two, called Sirius A, is orbited by a faint white dwarf called Sirius B. It takes these two stars about 50 years to orbit each other. They are also moving through space together. Sirius is expected to increase in brightness as it moves closer to our Solar System. About the same time it reaches its peak magnitude, 60,000 years from now, it will also have slid south in our sky, becoming our southern Pole Star. After that, it will pass us by, becoming fainter with distance. 210,000 years from now, Vega should be our brightest star.

Sirius is known as the "Dog Star" because it is the brightest star in the constellation Canis Major, Latin for ‘big dog,’ and one of two dogs that follow on the heels of Orion the hunter. The best time to see Orion is in winter, when he chases Taurus across the night sky. During the summer, he is too close to the sun and is a daylight constellation, hidden behind the blue sky caused by the refraction of the sun’s rays through our atmosphere.

Ancient Greeks and Romans noticed that Sirius closed in on the Sun in mid-summer. They believed that its heat combined with the Sun’s heat to produce sultry summer weather. They thought this conjunction brought ill fortune in the guise of drought, fever, and general discomfort. Roman poet Virgil wrote that Sirius “brings drought and plague to frail mortals” when it rises.

Actually, Sirius brings little light to our Earth and no heat whatsoever.  The intense heat of the dog days of summer is actually caused by the Earth’s tilt and by "thermal lag." This is the delay it takes for the land and oceans to fully heat up after the longest day of the year, on June 21.

Yesterday morning I had to get up at 4 am so I could get my husband to the airport by 5:30. I was walking the dog in the dark when I noticed the Perseids, a fabulous cluster of stars, in the eastern sky. I looked a little below them and saw the V of Taurus and below it, lying on his side right on the horizon, was Orion. If Orion was rising, his faithful hunting dogs couldn’t be far behind, but low enough that they would still be lost in the light of the Sun. The dog days were not yet over, but they soon would be.

Now if only we could say the same for the hot weather.

Jennifer Bohnhoff has always had her head in the stars. She learned the constellations from her father when she was a very young child. She took her first astronomy class when she was still in Junior High and was on the staff of the UNM observatory when she took astronomy classes there during college. She writes historical and contemporary fiction for middle grade readers through adults. You can learn more about her here, on her website.

Incidentally, she and her husband just adopted their own major canine two weeks ago. His name is Rommel, and he is  a 4 1/2 year old (suposedly, but who knows?!) Rottweiler (again, supposedly) who'd been in the pound since April. So far, he hasn't left any messes, chewed on any furniture, stolen any food off the counter, and he's slept through the night without getting on either the bed or sofa. Jennifer's only concern is that he's terrified of outsiders and not friendly toward others at all. She's hoping that he will gain confidence and be more accepting of others. After all, he's a big guy, so what does he have to be afraid of?