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Records tagged “history”
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- The Gregorian leap year rule: divisible by 4, except centuries not divisible by 400In the Gregorian calendar introduced in 1582, a year is a leap year if divisible by 4, except century years, which must be divisible by 400. So 2000 was a leap year but 1900 was not; the mean calendar year is 365.2425 days.
- Why historical sources give two different dates for the same event: Julian vs Gregorian calendarsCountries adopted the Gregorian calendar at different times, from 1582 to the 20th century, so sources may record one day under two dates. Isaac Newton, for example, was born on 25 December 1642 in the Julian calendar, which is 4 January 1643 in the Gregorian.