Everyone talks about “dog days” but few know what the expression means. Some will say that it signifies hot sultry days “not fit for a dog;” others say it’s the weather in which dogs go mad. But the dog days are defined as the period from July 3 through August 11 when the Dog Star, Sirius, rises in conjunction (or nearly so) with the Sun. As a result, some felt that the combination of the brightest luminary of the day (the Sun) and the brightest star of night (Sirius) was responsible for the extreme heat that is experienced during the middle of the summertime. Other effects, according to the ancients, were droughts, plagues, and madness.
A more sensible view was put forward by the astronomer Geminus around 70 B.C. He wrote: “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.”
In ancient Egypt, the New Year began with the return of Sirius. It was, in fact, the “Nile Star” or the “Star of Isis” of the early Egyptians. Interestingly, some 5,000 years ago, this “heliacal rising” (appearing to rise just prior to the Sun) occurred not in August, as is the case today, but rather on, or around June 25. When they saw Sirius rising just before the Sun, they knew that the “Nile Days” were at hand. Its annual reappearance was a warning to people who lived along the Nile River. The star always returned just before the river rose, and so announced the coming of floodwaters, which would add to the fertility of their lands. People then opened the gates of canals that irrigated their fields.
Priests, who were the calendar keepers, sighted the first rising of the Dog Star from their temples. At the temple of Isis-Hathor at Denderah is a statue of Isis, which is located at the end of an aisle lined by tall columns. A jewel was placed in the goddess’ forehead. The statue was oriented to the rising of Sirius, so that the light from the returning Dog Star would fall upon the gem. When the priests saw the light of the star shining upon the gem for the first time, they would march from the temple and announce the New Year. In the temple appears the inscription: “Her majesty Isis shines into the temple on New Year’s Day, and she mingles her light with that of her father Ra on the horizon.”
Sometime around or soon after August 12th, just before sunrise, Sirius might again be glimpsed rising just above the southeast horizon for those living in mid-northern latitudes. At far southerly latitudes, Sirius becomes conspicuous sometime during the second week of August, twinkling above the horizon at dawn. Sirius is the brightest star of the constellation Canis Major, the “Greater Dog” in Latin. According to Burnham’s Celestial Handbook other names for it include “The Sparkling One” or “The Scorching One.” The star appears a brilliant white with a tinge of blue, but when the air is unsteady, or when it is low to the horizon as it is now, it seems to flicker and splinter with all the colors of the rainbow. At a distance of just 8.7 light years, Sirius is the fifth-nearest known star. Among the naked-eye stars, it is the nearest of all, with the sole exception of Alpha Centauri.