Although the long, hot and muggy days of August might serve up weather that is not "fit for a dog", the phrase "Dog Days of Summer" have nothing to do with your pet's health or comfort. So where did this canine appellation originate? The answer lies in the stars.
More specifically, the answer lies in the constellation Canis Major, or The Greater Dog. The brightest star in this constellation is Sirius, commonly called "the dog star". Sirius is the fifth nearest star to Earth at a mere distance of 8.6 light years (that's more than 50 trillion miles). The measure of a star's brightness is called magnitude, and the lower the number, the brighter the star. Sirius has a magnitude of -1.44, the lowest of any star. Sirius is the brightest star in the night sky, outshone only by our Moon, and the planets Mars, Mercury, Jupiter and Venus.
In July and early August, Sirius rises in the sky before the Sun and can easily be seen in the lower part of the sky if the sky is clear and without obstruction. The early Romans observed that Sirius rose and set with the Sun, and believed that because of its brightness, Sirius added its warmth to the Sun's heat, causing the long stretch of hot and sultry days of late summer. They also believed it could bring on droughts, make humans weak and feverish, and cause madness in dogs. Homer, in his Iliad, referred to Sirius as Orion's dog and described the appearance of Sirius with this passage:
“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.”
Because Sirius sits low in the sky, with its light shining through Earth's atmosphere, its normally blue-white light may change to other colors. When the air is unstable, its light may seem to flicker. In modern times, Sirius has been mistaken for a UFO, due to its brightness and twinkling.
The name Sirius is generally considered to be taken from the Greek , meaning burning or scorching. Some have suggested the name may have been appropriated and had some connection to the Egyptian god Osiris. The Egyptians noted that the appearance of Sirius in the sky coincided with the flooding of the Nile, and called it the “watchdog”. Sirius has various names and connotations in many cultures.
The Dog Days are traditionally said to be the 40 days between July 3 and August 11. During this time, Sirius rises with the Sun. For stargazers, to see Sirius in the night sky, look for Orion and follow an imaginary line south from Orion's belt.