A long time ago on a continent far, far away...
Priam saw him first, with his old man's eyes,
A single point of light on Troy's dusty plain.
Sirius rises late in the dark, liquid sky
On summer nights, star of stars,
Orion's Dog they call it, brightest
Of all, but an evil portent, bringing heat
And fevers to suffering humanity.
Achilles' bronze gleamed like this as he ran.
The Dog Days of Summer are said to be the hottest and most uncomfortable days of the season.
The term comes down to us from the Greeks and Romans, who noted that the onset of the most intense summer heat -- along with drought and intense thunderstorms -- seemed to coincide with the late-summer arrival of Sirius. The Dog Star.
Sirius is part of the constellation Canis Major, or Great Dog, and represents the shoulder (?) of the big dog. It is also the brightest star in the night sky (and in fact is a double-star).
The Greeks described Canis Major as the companion of Orion, following the mighty hunter through the night sky. Orion is located on the celestial equator and due to the geometry of Earth's orbit is absent below the southeasterly horizon in spring and through much of the summer. It begins to rise late at night in August.
Sirius and the Great Dog are actually located in the southern celestial hemisphere, just below the celestial equator, and appear to trail "behind" Orion as the stars make their nightly swing through the sky.
The Greeks -- and later the Romans -- noted the brightness of Sirius and wondered if that blazing bright star was responsible for the stifling summer heat which arrived at about the same time.
|Dotted Gayfeather (Liatris puncata)|
It was a good hypothesis. Now that we're a bit more astronomically accomplished, we've discovered that Sirius A is about twice the size of our own sun, twenty-five times more luminous, and is one of our very near galactic neighbors, being only about 8.6 light years (50,556,178,209,379 miles) distant. Today we know that Sirius is much to far away to add heat to our planet, but you can understand and appreciate the reasoning of the ancients.
As with everything else about climate, the actual warmth of the Dog Days is variable. We can imagine that late summer featured relatively warm and still periods during the last ice age -- roughly 15,000 to 110,000 years ago, but it's unlikely that anyone complained about the heat at that time.
Furthermore, the actual onset of late-summer heat isn't linked to a particular calendar day. The Dog Days can arrive any time between mid-July and early September.
And finally (at least for this post), the Dog Days are a period of heat and stillness which are relatively hotter than the rest of the season, but there's no absolute thermometer reading which defines the heat. During the Little Ice age (Ca. 1300-1850) the mercury may have only touched 75 degrees during the Dog Days, while 115-120 degrees might have been the norm during the Dust Bowl era.
|Rubber Rabbitbrush (Chrysothamnus nauseosus) and Blue Grama (Bouteloua gracilis).|
And all of the preceding horse$#!+ is by way of introducing this...
Dang it's hot.
It's not terribly hot. It's been a relatively cool summer in fact. June and July were slightly warmer than usual but also featured cool spells as weather fronts moved through. August was more uniform, with fewer weather systems to mix up daily temperatures, but those daily temps were cooler than average for the month.
As August began to fade, though, the warmth increased and a pressure ridge kept the nearby atmosphere stable.
|Fringed Sagewort (Artemisia frigida) in the act of flowering.|
Thus far in September the pattern is holding. Today the mercury is expected to reach into the upper 90's, which is quite warm for the ninth month of the year but far from unheard of. The relative stillness of the air has also allowed a lot of wildfire smoke to drift in from Montana.
So it's been a little bit uncomfortable from my perspective. A little too hot and still, with heat lingering late into the evening. As Dog Days go, however, these have been quite mild. In two weeks time I'll be vexed by morning coolness and perhaps even frost. As summer slowly fades, so does the time of easy living.
It's also time for farmers to plant winter wheat. Looks like work to me.