**Since the ancient times, people has been
interested in marking time. Thru knowledge of the positions of the
sun and the stars, as well as seasonal events, the length of a year may be computed. The
length of a year is approximately 365.2425 days.**
**The Julian Calendar, developed
during the time of Julius Ceasar, was based on the approximation that the
length of year was 365.25 days. Thus, every 4 years, an extra day
was needed to compensate for the extra time needed to fully complete the
period of
earth's revolution around the sun.**
**Because the approximation used for
the Julian calender year was 365.25, instead of the more accurate number of 365.2425,
every one hundred year on the Julian Calendar introduces an unnecessary
extra leap day on the calendar. This causes inaccuracy in prediction
the Spring Equinox, which is important in the determination of the date of Easter.
These small inaccuracies added up over the centuries, and caused the
celebration of Easter to occur at a later time in spring.**
**The Gregorian Calendar was introduced in 1582, when
Pope Gregory XIII modified the Julian calendar. The purpose of this
modification was to restore the date of Easter to
spring. Unlike the Julian Calendar, the years divisible by 100 in
the Gregorian Calendar are not leap years, unless they are divisible by
400. Thus, the years 1700, 1800 and 1900 were not leap years, while
the years 1600 and 2000 were.**
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