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Aluise Baldassar Lilio. Portrait of the Italian physician and astronomer Aluise Baldassar Lilio (1510-1576). Lilio proposed a major revision of the calendar. In 1582, Pope Gregory XIII approved Lilio's proposals and the new calendar became known as the Gregorian calendar. Lilio proposed to drop ten days from the calendar and that century years not divisible by 400 should not be leap years. The changes were necessary because the old calendar (the Julian calendar) year was 11 minutes and 14 seconds longer than the solar year. This meant that by 1582 church holidays were not occurring in the appropriate seasons.
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