The phrase dog days refers to the sultry days of summer. In the Northern Hemisphere, the dog days of summer are most commonly experienced in the months of July and August, which typically observe the hottest summer temperatures. In the Southern Hemisphere, they typically occur in February and March, in the midst of the austral summer.
The Romans referred to the dog days as diēs caniculārēs and associated the hot weather with the star Sirius. They considered Sirius to be the "Dog Star" because it is the brightest star in the constellation Canis Major (Large Dog); this linkage first appeared in the Greek poem Phaenomena by Aratus (~310-260 BC) while Sirius's association with summer heat is found in an earlier Greek poem, Works and Days by Hesiod in ~700 BC. Sirius is also the brightest star in the night sky. The term "Dog Days" was used earlier by the Greeks (see, e.g., Aristotle's Physics, 199a2).
The Dog Days originally were the time of the year when Sirius rose just before or at the same time as the sun (heliacal rising, in Conjunction (astronomy) with), which is no longer true, owing to precession of the equinoxes.
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 24 through August 24, or, alternatively, from July 23 through August 23. 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 3 and ending August 11, 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.[dubious ]
According to the 1552 edition of the The Book of Common Prayer, the "Dog Daies" begin July 6 and end August 17. 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 7 and end August 18. But this is noted as a misprint and the readings for September 5 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 6 and ending on September 5. 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 5, 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.
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 16 and end on August 24.
The Book of Common Prayer would have provided the official liturgical calendar for Jamestown, Virginia, from 1607 so it may be assumed that the Dog Days likely have been known in the New World at least since that time.
In many languages, mainly the Romance languages, the word canicula and its derivatives designate today the summer school and work holidays.
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- Sirius: Brightest Diamond in the Night Sky By Jay B. Holberg, 2007 | https://books.google.com/books?id=zc3zw-YgOPkC&pg=PA33&lpg=PA33&dq=Aristotle+Physics++sirius&source=bl&ots=bMtFGpXjO5&sig=RwnO7cI9u52P7cgSN0yYSzMJnvw&hl=en&sa=X&ei=TekEVd2aKoG-ggTwnoGACw&ved=0CCcQ6AEwAg#v=onepage&q=dog&f=false
- Brady, J: "Clavis Calendaria", vol. II, page 89. Nichols, Son, and Bentley, 1815.
- Booty, John (1976). The Book of Common Prayer, The Elizabethan Prayer Book. Folger Shakespeare Library, Washington DC: Folger Books. pp. 42–44. ISBN 978-0-918016-58-4.