1538, from L.
dies caniculares, from Gk. (the star was also known as
kyon seirios) are around the time of the heliacal rising of
Sirius (q.v.), the Dog-star, noted as the hottest and most unwholesome time of the year; usually July 3 to Aug. 11, but variously calculated, depending on latitude and on whether the greater Dog-star (Sirius) or the lesser one (Procyon) is reckoned. The heliacal rising of Sirius has shifted down the calendar with the procession of the equinoxes; in ancient Egypt c.3000 B.C.E. it coincided with the summer solstice, which was also the new year and the beginning of the inundation of the Nile. The "dog" association apparently began here (the star's hieroglyph was a dog), but the reasons for it are obscure.
