The Dog Days originally were the days when Sirius rose just before or at the same time as the sun (heliacal rising), which is no longer true, owing to procession of the equinoxes. The Romans sacrificed a red dog in April to appease the rage of Sirius, believing that the star was the cause of the hot, sultry weather.
Dog Days were popularly believed to be an evil time "the Sea boiled, the Wine turned sour, Dogs grew mad, and all other creatures became languid; causing to man, among other diseases, burning fevers, hysterics, and phrensies." according to Brady’s Clavis Calendaria, 1813.
In Ancient Rome, the Dog Days ran from July 24th through August 24th, or, alternatively, from July 23 through August 23rd. In many European cultures (German, French, Italian) this period is still said to be the time of the Dog Days.
The Old Farmer's Almanac lists the traditional period of the Dog Days as the 40 days beginning July 3rd and ending August 11th, coinciding with the ancient heliacal (at sunrise) rising of the Dog Star, Sirius. These are the days of the year with the least rainfall in the Northern Hemisphere.
According to the 1552 edition of the The Book of Common Prayer, the "Dog Daies" begin July 6th and end August 17th. But this edition, the 2nd book of Edward VI, was never used extensively nor adopted by the Convocation of the Church of England. The lectionary of 1559 edition of the Book of Common Prayer indicates: "Naonae. Dog days begin" with the readings for July 7th and end August 18th. But this is noted as a misprint and the readings for September 5th indicate: "Naonae. Dog days end". This corresponds very closely to the lectionary of the 1611 edition of the King James Bible (also called the Authorized version of the Bible) which indicates the Dog Days beginning on July 6th and ending on September 5th. A recent reprint of the 1662 edition of the Book of Common Prayer contains no reference to the Dog Days.
Given that the traditional period of the Dog Days is Forty Days [A scripturally significant number], the error could be read as being September 5th as the time between July and August does correspond to that number of days and would also be in line with the common European tradition.
Please note: Due to introduction of the modern Gregorian Calendar, 10 days must be added to each of the 16th and 17th Century dates referenced above for them to correlate correctly with modern-day dates as concerns astronomical observations and climate. Therefore the Dog Days would begin on July 16th and end on August 24th
The Dog Star Sirius
In ancient Egypt, Sirius was known as Sopdet (Greek: Σῶθις, or Sothis). Sothis was identified with Isis, the goddess who was part of the triad with her husband Osiris and son Horus. The hieroglyph for Sothis has a star and a triangle.
Egyptians based their calendar on the heliacal rising of Sirius in the era of the Middle Kingdom. The star’s rising marked the beginning of the new year and the event was celebrated with a festival known as “The Coming of Sopdet.”
The day Sirius became visible just before dawn after moving far enough away from the Sun to not be lost in the Sun’s glare signalled the flooding of the Nile every year. This would happen just before the summer solstice and the star would be visible before sunrise after being absent from the skies for about 70 days.
Sirius and Canis Major constellation the 70-day absence symbolised Isis and Osiris’ passing through the Egyptian underworld, the Duat. The flooding of the Nile brought fertility to the land when the star appeared, and Egyptians associated Isis with both the inundation, fertility and the new year. They called Sirius the Nile Star.
The Egyptians believed that Sirius caused the floods and they noted that the star’s heliacal rising occurred every 365.25 days rather than 365 days. The correction in the length of the calendar year was eventually incorporated in the Julian calendar.
The Egyptians also saw Sirius as the doorway to the afterlife and would not bury their dead during the 70 days the star was hidden from view – the 35 days before and after Sirius conjuncted the Sun. They believed the doorway was closed when the star was out of view.
Several occult researchers believe that the Great Pyramid of Giza was constructed in perfect alignment with stars, particularly with Sirius and the three stars of the Orion’s Belt. Recent findings related to the pyramid’s mysterious air shafts have strengthened the theory of Sirius’ importance to Egyptians.
The Greeks noticed that the star’s appearance in the sky heralded the hot, dry summer season. Sirius was known to twinkle more in the early summer and the Greeks interpreted this as a malignant influence. The star was often described as “burning” in various texts, and the season it heralded became known as the dog days of summer.
On the island of Ceos, inhabitants would offer sacrifices to Zeus and Sirius to bring cooling breezes and, if Sirius rose clear, they would see this as a sign of good fortune. If the star was faint or misty, it foretold pestilence. Archaeologists found coins on the island dating from the 3rd century BC that featured dogs and stars with emanating rays.
The Romans, similarly, celebrated the star’s heliacal rising around April 25, and would sacrifice a dog and a sheep to the goddess Robigo in the hope that the star would not cause wheat rust on their crops that year. They called the hottest days of the summer summer dies caniculares and Sirius was known as Canicula, or “little dog.”
The star is associated with dogs in a number of cultures. Being the brightest star in the Greater Dog constellation, it was classically represented as one of the dogs of Orion, the Hunter. Homer calls the star “Orion’s Dog” in The Iliad. In ancient Greece, there was a belief that the star could make dogs behave abnormally during the summer.
The Chinese knew Sirius as the star of the “celestial wolf.” In anicent times, they visualised the constellations Puppis and Canis Major as a large bow and arrow, with the arrow tip pointed at the wolf.
Ancient Polynesians used Sirius for navigation, and saw it as part of the Great Bird constellation called Manu. The bright star Canopus in Carina marked the southern wingtip and Procyon in Canis Minor the northern one. The constellation divided the sky into two hemispheres, and the stars were used as latitude markers. The declination of Sirius matches the latitude of Fiji at 17°S, which means that the star passes directly over the islands every night.
To the Māori, the star marked the beginning of the winter season. They had the same name to describe both the star and the season: Takurua.
In Hawaii, Sirius was known as Ka’ulua, or the Queen of Heaven. The star’s culmination at the winter solstice was celebrated with an event every year.
In India, the star is sometimes known as Svana, the dog of Prince Yudhistira, who set out of a long journey to find the kingdom of heaven with his four brothers. The journey was a difficult one and, one by one, the brothers abandoned the search. When Yudhistira reached the gates of heaven, Lord Indra welcomed him, but would not let Svana enter. The prince told him that he himself would not enter if his faithful servant was denied entrance. This is what the Lord wanted to hear, and he then allowed them both through the gates.
In Sanskrit, the star is known as Mrgavyadha, or “deer hunter,” representing Rudra (Shiva), or as Lubdhaka, meaning “hunter.”
In Persian mythology and Zoroastrianism, Sirius is seen as Tishtrya and revered as the divinity bringing rain and fertility.
Sirius is mentioned in the Qur’an, where it is called the Mighty Star or Leader. The star’s other proper name, Aschere, is derived from Arabic.
Many indigenous peoples of North America associated Sirius with figures of dogs and wolves. The Blackfoot knew the star as “Dog-face,” Pawnee tribes of Nebraska called it the “Wolf Star” or “Coyote Star,” and the Cherokee saw Sirius and Antares in Scorpius constellation as dog-star guardians of the two ends of the Path of Souls. The Alaskan Inuit knew Sirius as “Moon Dog.”