Apple #682: Dog Days of Summer

It has finally turned humid this summer.  For weeks and weeks, the weather has been beautiful -- sunny, breezy, warm, and none of that oppressive humidity.  But a few days ago, we had a big fat thunderstorm, and it left a lot of that humidity behind.  Looks like it won't budge for the whole week, either.

Which makes me think, we have finally entered the Dog Days of Summer.

What does that mean, anyway?  I have always imaged it means this:



(Photo from Doggie Cakes)


(Photo by Snowlight at Flickr, sourced from Low Country Dog)


(Photo from The Pet Wiki)


The Dog Days of Summer: when the weather gets so hot, all the dogs are panting.

But no, that is not the correct definition.

• The Dog Days refers to the position of Sirius, the dog star (No, not Sirius Black), relative to the sun.

Sirius is the brightest star in the constellation Canis Major (Bigger Dog). It's just below Orion -- the 3 stars of Orion's belt point to it.  The story goes that Canis Major is Orion's hunting dog.
(Image from Space.com)

• Ancient Romans noticed that during the hottest time of the summer, the brightest star in the night sky -- Sirius -- was rising and setting roughly the same time as the sun. 

• Some people say the Romans thought that Sirius's conjunction with the sun was adding heat to the days, and that's why those particular days were hotter.  

• In reality, while Sirius is the brightest star in the sky, it is much too far away for its heat to have any impact on us.  

Sirius is larger and brighter and hotter than our sun -- though it's too far away for us to feel its heat.
(Image from Astro Bob)

• The Romans were pretty smart cookies, though, so they may have known this and simply been aware that the two were in the sky at the same time. 

• Ah, yes, here we are.  An astronomer named Geminus wrote, around 70 B.C., "It is generally believed that Sirius produces the heat of the 'dog days,' but this is an error, for the star merely marks a season of the year when the sun's heat is the greatest." 

• (So, Weather Channel and everybody else, quit making the Romans out to be a bunch of dummies.)

• Knowing that the two stars were in the sky at the same time, the Romans named that stretch of days the Dog Days of Summer. (Actually, the time period goes from about 15 days before the two rise together through 15 days after)

• Exactly what part of summer that happened is also now in question.  Because of the very slow change in the Earth's orientation on its axis, when Sirius rises with the sun now is slightly different than when it rose back then. 

• Some say it used to happen from July 23 though August 23, or thereabouts.

• Now, however, the Farmer's Almanac says the Dog Days officially happen each year from July 3 through August 11, and everybody more or less goes along with that.

• But the site EarthSky.org says that Sirius is visible in the pre-dawn sky this year as of August 26.  So it seems the ancient Romans were closer in their calculations way back when than we are with our Farmer's Almanac today. 

• You kids with your smart phones, you've probably got an app that allows you to point your phone at the sky and it will tell you where the constellations are.  If you don't, this app called Star Walk ($2.99) supposedly does just that. Get an app like this, and you can see for yourself where Sirius is, and whether we're actually in the Dog Days or not.

• (I know, he fell through the portal and he isn't coming back.)

Sources
Columbia Encyclopedia via Factmonster, Dog Days of Summer
The Weather Channel, Why Are They Called the "Dog Days" of Summer?
Farmer's Almanac, Weather Wisdom for August: Dog Days of Summer
Theweatherprediction.com, What Are the Dog Days of Summer?
The Sacramento Bee, Pet Connection: Do you know the story behind 'dog days of summer'? August 23, 2014
Space.com, Doorstep Astronomy: Sirius Gets Serious and Sirius: Brightest Star in Earth's Night Sky