High School Math

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Friday, January 28, 2005

Gregorian Calendar


The calendar currently in worldwide use is the Gregorian Calendar. It has a year of length 365.2425 days. The Gregorian calendar is a modification of the Julian calendar in which leap years are omitted in years divisible by 100 but not divisible by 400. By this rule, the year 1900 was not a leap year (1900 is divisible by 100 and not divisible by 400), but the year 2000 was a leap year (2000 is divisible by 400). This gives an exact number of weeks per 400-year cycle.

The Julian calendar was replaced by the Gregorian Calendar in 1582. Pope Gregory XIII decreed that the day after October 4, 1582 would be October 15, 1582, the Catholic countries of France, Spain, Portugal, and Italy complied. Various Catholic German countries (Germany was not yet unified), Belgium, the Netherlands, and Switzerland followed suit within a year or two, and Hungary followed in 1587.

Because of the Pope's decree, the reform of the Julian calendar came to be known as the Gregorian calendar. However, the rest of Europe did not follow suit for more than a century. The Protestant German countries adopted the Gregorian reform in 1700. By this time, the calendar trailed the seasons by 11 days. England (and the American colonies) finally followed suit in 1752, and Wednesday, September 2, 1752 was immediately followed by Thursday, September 14, 1752.

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