1640 (MDCXL)
was a leap year starting on Sunday of the Gregorian calendar and a leap year starting on Wednesday of the Julian calendar, the 1640th year of the Common Era (CE) and Anno Domini (AD) designations, the 640th year of the 2nd millennium, the 40th year of the 17th century, and the 1st year of the 1640s decade. As of the start of 1640, the Gregorian calendar was
10 days ahead of the Julian calendar, which remained in localized use until 1923.
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