Dog Days
From Free net encyclopedia
- For Dog Days, the Swedish 1970 movie, see Rötmånad (film).
Dog Days or dog days of summer are typically the hottest and most humid times of the year. These days usually fall between July and early September but the actual days vary greatly from region to region, depending on latitude and climate. Dog days can also to define a time period or event that is very hot and/or stagnant. Also many religious cultures believe that dog days are holy.
They get their name because the period this occurs is often during the time the star Sirius, known as the Dog Star (and the brightest star of all as seen from Earth), both rises after, and sets before, the Sun and is hence lost in the latter's glare. This period of invisibility, for Northern Hemisphere observers, is caused by the fact that the position of Sirius in the celestial sphere is well to the south of the ecliptic. The ancient Egyptians observed that the annual flooding of the Nile Delta would typically occur shortly after the star returned to view immediately before sunrise, taken to be around mid-August in the current calendar.
By contrast, "dog days" as defined herein do not occur at all in the Southern Hemisphere, for there even when the star is least favourably placed for viewing (around July 1), it will be briefly visible both in the east before dawn and again in the west after dusk — and throughout most of Antarctica Sirius is circumpolar; that is to say, constantly above the horizon.
The further north one goes, the longer Sirius remains invisible each year, and beyond a latitude of approximately 74°N the star never appears above the horizon at all, making the colloquial, modern use of the term "dog days" to refer to the hot days of summer less than universally accurate.
The term itself was coined by the ancient Romans, who called these days caniculares dies (days of the dogs) after the constellation of Canis Major, (bigger dog) within which Sirius (α Canis Majoris) is found. As the hottest and most humid days of summer generally coincided with the period where Sirius rose/set with the sun, they believed that heat from Sirius was increasing the heat of the sun.
In 2005 the dog days fall between July 3 and August 11, according to the Old Farmer's Almanac.
According to the 1552 Book of Common Prayer the "Dog Daies" begin on 6 July and end on 4 September.
See also
- Sirius
- Dog Day Afternoon, a 1975 movie.
- The "Dog day cicadas".
- Hundstage (English Dog Days), a film by Ulrich Seidlda:Hundedagene