See also Aloysius Lilius
(Creator of the Gregorian
Calendar) »
The need for the Gregorian
reform stemmed from the fact
that the Julian calendar
system assumes time between
vernal equinoxes is 365.25
days, when in fact it is
about 11 minutes less.
The accumulated error
between these values was
about 10 days when the
reform was made, resulting
in the equinox occurring on
March 11 and moving steadily
earlier in the calendar.
Since the equinox was tied
to the celebration of
Easter, the reform in the
calendar was undertaken by
the Roman Catholic Church.
The
Gregorian calendar reform
contained two parts, a
reform of the
Julian calendar as used
up to Pope Gregory's time,
together with a reform of
the lunar cycle used by the
Church along with the Julian
calendar for calculating
dates of
Easter.
The
reform was a modification of
a proposal made by the
Calabrian doctor
Aloysius Lilius (or
Lilio). Lilius'
proposal included reducing
the number of leap years in
four centuries from 100 to
97, by making 3 out of 4
centurial years common
instead of leap years: this
part of the proposal had
been suggested before by,
among others,
Pietro Pitati. Lilio
also produced an original
and practical scheme for
adjusting the
epacts of the moon for
completing the calculation
of Easter dates, solving a
long-standing difficulty
that had faced proposers of
calendar reform.
See also Aloysius Lilius
(Creator of the Gregorian
Calendar) »
