Dog Days

From Academic Kids

The Dog Days are the period during which 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.

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.

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 term itself was coined by the ancient Romans, who called these days caniculares dies after the constellation of Canis Major, within which Sirius (α Canis Majoris) is found.

See also

de:Hundstage nl:Hondsdagen

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