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| | cmcmath : A Perpetual Calendar: Some Lessons in History and Mathematics |
 | | The Gregorian calendar, the one we use now, was promulgated in 1582 when the vernal equinox occurred on March 11. |
 | | Because the old Julian calendar was 3/4 of a day too long per century, the new Gregorian calendar skipped the leap year in three out of four century years and created what could be called "leap centuries." By the new calendar, 1600 was a leap year, but 1700, 1800, and 1900 were not. |
 | | It adopted the Gregorian reforms, moved the start of the year back from March 25 to January 1, and set September 2, 1752, Julian, as the date of change. |
| www.cmc-math.org /PerpetualCalendar (1474 words) |
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