The Christian Calendar
The solar or tropical year is the time needed forthe earth to orbit the sun from a spring equinox to the following one.This period lasts approximately 365,24219 days, that is to say 365days 5 hours 48 minutes and 45 seconds…but it tends to shrinkwith time.
The solar or tropical year is the time needed for
the earth to orbit the sun from a spring equinox to the following one.
This period lasts approximately 365,24219 days, that is to say
365 days 5 hours 48 minutes and 45 seconds…but it tends to
shrink with time.
In the year 45 B.C. Julius Cesar
introduced a reform so as to change the calendar and adjusted it
to the changing of the seasons: indeed it was established that
in a four-year period, three would last 365 days and the other
one would last 366 days. The 366-day year is called bissextile
as the extra day was inserted six days before the calends
(that’s the beginning) of March (in Latin "bis sexto die ante Kalendas
Martias").
In 325 the council of Nice established the
21st of March as the spring equinox date. The Julius calendar
wasn’t perfect as it meant that every year would last 365,25
days. However, the solar year lasts approximately 365,24219
days. It resulted in a difference of one day every 128 years
(1/(365,25 – 365,24219) ~ 128). The difference in the course of
time created a slight lag of seasons. It resulted in a negative
calculation of Easter, strictly linked to the spring equinox.
On February 24th 1582 with the Papal bull “Inter gravissimas” Pope
Gregorio XII tried to eradicate the errors of the Julian calendar,
according to the council of Trento (1545-1563), accepting the proposal
of the physician Aloysius Lilius to have in common, that is to
say not bissextile, the secular years that, divisible by 400
would have no extra time remaining.
Thus the years
1600 and 2000 were bissextile but not the years 1700, 1800,
1900. Then some days that were accumulated by error with time
had to be erased because seasons were not well timed: thus it was
established that the day after October 4th 1582 was Friday 15th of
October 1582. The period was chosen since there were no celebrations
held at the time. For the ten days erased this calculation was
made: {(1582-325)/128}~ 10.
Not all states adopted
the Gregorian Calendar at the same time: the first states were
Italy, Spain, Portugal and Poland, followed by the other
catholic countries (1582-1587), then, by the protestant
countries (1700-1753). It was finally adopted by all, with some
exceptions, between 1915 and 1949.
However, the Gregorian
Calendar still had some errors. 97 years were considered
bissextile every 400 years and therefore the medium year would
last 365,2425 days. In reality the tropical year lasts
approximately 365,24219 days. It resulted in a difference of one day
every 3300 years (1/(365, 2425 – 365, 23219) ~ 3300). Some astronomers
also proposed to consider non bissextile, the years multiple of
4000.
The Holy Easter
According to a biblical reconstruction, Easter occurs on the Sunday
following the first full moon after the spring equinox. The Council of
Nice set up this rule in 325.
Thus Easter can be comprised between the 22nd of March and the 25th of
April inclusive. Indeed if the 21st of March was a Sunday with a full
moon, Easter would be the 22nd of March. If there was a full moon on
the 20th of March, we would wait until the 18th of April to have
another one. Therefore if the 18th of April was a Sunday, Easter would
be the following Sunday, the 25th of April.
Therefore Easter is a movable feast. With the Gregorian Calendar we
would wait 5.700.000 years before the Easter date would be repeated
with the same frequency!
Download
GoodTime! is a freeware software that calculates
the date of the Holy Easter from the year 1 to the year 9999. GoodTime!
is also a perpetual calendar that can find the week day and the month
of a date between 1 and 9999. GoodTime! calculates the date and days
of Easter according to the Julian Calendar until the 4th of October
1582. It uses the Gregorian Calendar for the dates following the 15th
of October 1582.
GoodTime! is a freeware software, therefore it can be used and given
for free if the author’s information is still present!
You can send an e-mail to this address:
goodtime@davidemonti.com
However, the first celebration of Easter was officially in the year
326 after the council of Nice occurred. Moreover the Gregorian
Calendar was correctly efficient until approximately 4100. The Easter
dates before the year 326 and the days following the year 4100 are
then merely indicated.
GoodTime! can be installed on the following systems:
Win98/Me/NT(SP4)/2000/XP/7/8/10 con Microsoft .NET Framework
