Isaac Newton’s birthday is 25 Dec.
Of course, it’s more complicated than that.
During Newton’s lifetime, two calendars were in use in Europe: the Julian (“Old Style”) calendar in Protestant and Orthodox regions, including Britain; and the Gregorian (“New Style”) calendar in Roman Catholic Europe. At Newton’s birth, Gregorian dates were ten days ahead of Julian dates: thus his birth is recorded as taking place on 25 December 1642 Old Style, but can be converted to a New Style (modern) date of 4 January 1643.
