The Perpetual Calendar
The Story of Why 10 Days Were Dropped in 1582

1582 - Pope Gregory XIII Orders Calendar Changes, and Issues The Drop Decree

In 1582, a special Vatican committee called for by Pope Gregory XIII, the then-reigning Supreme Pontiff of the Roman Catholic
Church, announced that due to inaccuracies in the Julian Calendar, in use for over fifteen (15) centuries, many annual holidays
and special celebrations of the church were off by an estimated ten (10) days. Pope Gregory accepted the committee's findings
and ordered that adjustments be made to the older Julian calendar. The most significant change resulted in Century Years
such as 1700, 1800, 1900, 2100, 2200, 2300, etc., which are not divisible by 400, to be only regular 365-day long years, rather
than 366-day Leap Years -- in other words, no observance of the February 29th Leap Day in those particular years. From then
on, only Century Years such as 1600, 2000, 2400, etc., whch are divisible by 400, would be 366-day Leap Years. The years in
each century divisible by four (4) -- xx04, xx08, xx12, etc., thru xx96 -- would continue to be 366-day Leap Years.

The end result was what we today call the Gregorian Calendar, also referred to as the Perpetual Calendar. Over continuous
periods of 400 years each, the Gregorian calendar has exactly 146,097 days and 20,871 seven-day weeks. A 400-year period
will always begin on Saturday January 1st (in 1600, 2000, 2400, 2800, etc.), and will always end on Friday December 31st
(in 1999, 2399, 2799, 3199, etc.).

With the calendar adjustments now completed, the only remaining issue was how to handle the accumulated error of ten (10)
days. Pope Gregory XIII's solution was a most radical one. In the month of October 1582, the very last day of Julian calendar
observance would be Thursday October 4th. Then the next day would be Friday October 15th, the first day of the revised
Gregorian-Perpetual Calendar. This particular ruling would not be a popular one, especially among those engaged in any
commercial business ventures. To ease the shock of transition, some papal advisors suggested that the calendar revisions
should be phased in over a broad period of time. However, Pope Gregory would not agree to this, ordering that the revised
calendar system was to be put into effect right away -- and so it was.

Although more accurate than the older Julian Calendar, the Gregorian Calendar is claimed by some observers to have an
error of one full day, occuring every 4000 years. If this is so, then in the A.D. years of 4000, 8000, 12000, etc. there would
be -NO- observance of the February 29th Leap Day. However, this particular matter has not as yet been officially dealt with.

Some Possible Alternatives Never Used
We will now suppose that Pope Gregory chose instead to approve a phase-in period of some kind. Presented
below, along with the actual sequence of events, are two possible alternative phase-in period scenarios.
A: Actual Year Calendar Sequence, 1580 to 1629,
   as ordered by Pope Gregory XIII

  1580, 13    1590,  2    1600, 14    1610,  6    1620, 11
  1581,  1    1591,  3    1601,  2    1611,  7    1621,  6
  1582, 2/6   1592, 11    1602,  3    1612,  8    1622,  7
  1583,  7    1593,  6    1603,  4    1613,  3    1623,  1
  1584,  8    1594,  7    1604, 12    1614,  4    1624,  9
  1585,  3    1595,  1    1605,  7    1615,  5    1625,  4
  1586,  4    1596,  9    1606,  1    1616, 13    1626,  5
  1587,  5    1597,  4    1607,  2    1617,  1    1627,  6
  1588, 13    1598,  5    1608, 10    1618,  2    1628, 14
  1589,  1    1599,  6    1609,  5    1619,  3    1629,  2
In 1582, Year Calendar-2 is used up thru October 4th, when Pope Gregory XIII orders the next 10 days to be
dropped immediately. As a result, October 15th becomes the first day after October 4th, and Year Calendar-6
is used from October 15th to the end of 1582.


B: Alternative Year Calendar Sequence, 1580-1629
    Observance of Leap Day February 29 omitted every four
    years from 1584 to 1620.
             
  1580, 13    1590,  3    1600,  6    1610,  2    1620,  5
  1581,  1    1591,  4    1601,  7    1611,  3    1621,  6
  1582,  2    1592,  5    1602,  1    1612,  4    1622,  7
  1583,  3    1593,  6    1603,  2    1613,  5    1623,  1
  1584,  4    1594,  7    1604,  3    1614,  6    1624,  9
  1585,  5    1595,  1    1605,  4    1615,  7    1625,  4
  1586,  6    1596,  2    1606,  5    1616,  1    1626,  5
  1587,  7    1597,  3    1607,  6    1617,  2    1627,  6
  1588,  1    1598,  4    1608,  7    1618,  3    1628, 14
  1589,  2    1599,  5    1609,  1    1619,  4    1629,  2
In Alternative Sequence B, no days are removed from 1582, and the observance of Leap Year and
February 29th is put aside in the period from 1584 to 1620.

Beginning 1621, Alternative Sequence B is equal with Actual Sequence A above. Observance of Leap Year
and February 29th is restored beginning 1624, and now the Gregorian Calendar is firmly in place.


C: Alternative Year Calendar Sequence, 1580-1629
    Transition from the Julian Calendar to the Gregorian
    Calendar in just ** THREE YEARS **.
              
  1580, 13    1590,  2    1600, 14    1610,  6    1620, 11
  1581,  1    1591,  3    1601,  2    1611,  7    1621,  6
  1582,  2    1592, 11    1602,  3    1612,  8    1622,  7
  1583,  3    1593,  6    1603,  4    1613,  3    1623,  1
  1584, **    1594,  7    1604, 12    1614,  4    1624,  9
  1585, **    1595,  1    1605,  7    1615,  5    1625,  4
  1586, **    1596,  9    1606,  1    1616, 13    1626,  5
  1587,  5    1597,  4    1607,  2    1617,  1    1627,  6
  1588, 13    1598,  5    1608, 10    1618,  2    1628, 14
  1589,  1    1599,  6    1609,  5    1619,  3    1629,  2
In Alternative Sequence C, no days are removed from 1582 or 1583.

In the years 1584, 1585 and 1586, the months of March, July and October have only 30 days each.
Also, the 1584 Leap Year day of February 29th is not observed. As a result, the ten days are dropped
over a period of three years, instead of the actual immediate dropping procedure of Sequence A above.

During this three-year period, each year -- 1584, 1585 and 1586 -- has only 362 days. By November 1st
of 1586, the desired reduction of ten days in just three years would be fully realized. From this point
onwards, the Gregorian Calendar System would now be firmly in operation.

You can click-on each one of the three years (shown herein in blue underlined text) and view
the calendar that would have been used in the particular year.

BONUS ... The Split 3/2 Calendar alternative plan.   (opens in new window/tab)
This alternative plan would have achieved the Julian-to-Gregorian transition in just nine years, albeit with
perhaps some confusion due to just this one year calendar being in place for eight consecutive years.


The Perpetual Calendar
The Story of Why 10 Days Were Dropped in 1582



Do you like this website?

If you wish to offer comments,
please click-on this image to sign my guest book.
Guestbook
Smart GB WebSite



Back To The Top Of This Page