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*The following is a translation of Pope Gregory XIII's De Anno et Eius Partibus, the 1582 document explaining changes to both the then-current Julian and liturgical calendars that resulted in the Gregorian Calendar. Although the changes are well-known--and better explained at the Wikipedia page on the calendar--I was surprised to find no English translation of this specific document on-line. I hope my meagre efforts below will help any English speakers interested in the original text.*

CONCERNING THE YEAR AND ITS DIVISIONS

The year has 12 months, 52 weeks plus one day: 365 days and about 6 hours; the sun in that space of time wanders thru the Zodiac. Four times six hours add up to a day every four years : Hence that year is called "Intercalary" or "bisextile".

ABOUT THE CORRECTION TO THE YEAR, ITS NECESSITY, AND THE GREGORIAN CALENDAR

As was said, the year contains 365 days and about six hours, but note that six hours is not an exact amount; since it lacks a certain number of minutes to complete six hours.

Despite the neglect of these minutes, each year was assumed to have an additional six hours beyond the 365 days: And so it happened that the minutes, which were added to the proper quantity each year, increased the extent of calendar time to the extent that ten days were added, which explains why the vernal equinox changed its position.

Addressing this mistake, Gregory XIII not only restored the date of the vernal equinox to its former position, since by order of the Nicaean Council he cut out ten days in the correction year 1582 for the sake of the next year, thereby setting up--according to the council--March 21st as the day of the full Easter moon (XIV lunam paschalem). But he also enacted a better method for the future such that the vernal equinox and the full moon of Easter would never move from their proper place.

So that the vernal equinox could be returned to March 21st, he ordered that 10 days in the month of October 1582 be removed; that after October 4th, the feast of St. Francis, the following day would not be the 5th, but the 15th of October. And that error which had crept in little by little over the years in a single moment was corrected.

To eliminate the error in the future, lest March 21st drift forward from the vernal equinox, Gregory ordered that the leap year (bisextilium) be continued every fourth year (as was the custom), except that in hundred-years, which had previously been leap-years, he wanted 1600 (the next) to be a leap year, but not all the hundred-years following that would be leap years; every 400 years the first three hundred-years would be without the bisextile day, but the fourth one would be a leap year. Thus 1700, 1800, and 1900 are not leap years, but the year 2000 by the usual custom would add a bisextile day, having a February 29th; and the same order of adding and intercalating a bisextile day would be preserved every 400 years thereafter.

THE FOUR TEMPORA

The four tempora are celebrated on the fourth and sixth day of the week and on saturday after the third sunday of Advent, after the first sunday of Lent, after Pentecost sunday, and after the third sunday of September.

CONCERNING THE CELEBRATION OF MARRIAGES

Matrimony can be celebrated at any time of the year. - 2 Let the solemn blessing of marriages be forbidden only from the 1st sunday of Advent to Christmas, inclusive, and from Ash Wednesday to Easter Sunday inclusive. - 3 The Ordinaries of places nevertheless can, during the aforementioned times and under sound liturgical laws, permit it as a substitute for ordinary time under just cause, if the spouses are notified to abstain from too much pomp.

CONCERNING 19-YEAR CYCLE OF THE GOLDEN NUMBER

The 19-year cycle of the golden number is the turnover of the number over 19 years from 1 to 19, and once it turns over it again returns to 1. By way of explanation: In the year 1577 the number of the 19-year cycle, which is called "golden", is 1; the following year 1578 is 2, and so on in the following years, always by one more, all the way to 19, the golden number which falls in the year 1595, after which, again, it returns to 1, such that in the year 1596 the golden number will be back to 1, and in 1597 it will be 2, etc.

As so, so that the golden number can be found in any selected year, the following table of golden numbers has been developed, the use of which begins from the corrected year 1582 inclusive, and remains forever. From it the golden number of any year after 1582 can be found in the following manner:

{TABLE}

Let the first number of the table (which is 6) be assigned to the year 1582, the second (which is 7) to the folowing year 1583, and so on continuously until it comes to the year whose golden number you seek, with a return to the start of the table each time you run thru it. For the number on which the proposed year falls shall give the golden number sought.

A BRIEF METHOD FOR KNOWING THE GOLDEN NUMBER OF EACH YEAR

To the number of the year about which you're inquiring, add just 1. For example: 1833 add 1; Then divide the sum by 19; whatever is the remainder, that will be the golden number of that year; if there is no remainder, the golden number will be 19.

CONCERNING EPACTS AND NEW MOONS

The epact is nothing other than the number of days by which the general solar year of 365 days exceeds the general lunar year of 354 days: Thus the epact of the first year is 11 days, since the general solar year exceeds the common lunar year by this amount; and indeed in the following year the new moons occur 11 days earlier than the first year. Because of this, the epact of the second year is 22 days, since in turn the solar year in that year exceeds the lunar year by 11 days which--when added to the 11 days of the first year--makes 22: And so then, once that year ends, the new moons occur 22 days earlier than in the first year. However, the epact in the third year is 3, because if 11 days are again added to 22, 33 is the result; if 30 days--which equals one intercalary month--are set aside, the remainder is three, and such is the next year. For all epacts increase by a repeated 11-day augment, except that 30 days are removed whenever they can be. Only when we come to the last epact 29 (corresponding to the Golden Number 19) is 12 added, then 30 removed from the total 41 to get back to the epact 11, as at the start. Thus, what happens is that the last intercalary month (when the Golden Number is 19) will be only 29 days. For if, like the other six intercalary months, it contained 30 days, the new moons would not return after 19 years to the same solar days, but rather would slip the march of months forward, and they would fall later than in the previous 19 years by one day. For which reason you will find in the book many things about a new method to restore the Roman calendar. However, there are 19 epacts and the same number of golden numbers, and they corresponded to these same golden numbers prior to the calendar correction as laid out in the following table:

{TABLE of Epacts Corresponding to Golden Numbers Prior to the Correction of the Calendar}

In truth, the 19-year cycle of golden numbers is imperfect; since new moons do not precisely return to the same days after 19 solar years, as mentioned; indeed, the Golden Number cycle will be innacurate after 19 epacts. For this reason it has been emended such that from now on in place of the Golden Number and the declared 19 epacts, we shall use 30 epact numbers, from 1 to 30 in increasing order, except the last epact--the one which is thirtieth in line--shall not be designated with a number but with the sign *, fro which reason no epact can be 30. However at various times out of these 30 epacts a changing set of 19 epacts corresponds to the 19 Golden Numbers, just as an equalization of solar and lunar year demands. ANd these 19 epacts progress such that running through to the same number 11, and as always 12 is added to this epact (correponding to Golden Number 19), the following epact will be seen to correspond to the Golden Number 1, by the reasoning given above. The following table shall make this clear, which lists Golden Numbers and corresponding epacts startign from the corection year 1582 (after the loss of ten days) all the way to 1700 inclusive. Though commonly epacts are changed in March, they are to be changed at the start of the year, at the same time as the Golden Number, in whose place this system of epacts supercedes

{TABLE of Epacts Corresponding to Golden Numbers from October 15th, 1582, the Correction Year (with ten days first removed) inclusive, to the year 1700 Exclusive}

And so if the epact for any year chosen needs to be found, the Golden Number of that year should be found in the top line of the table, which agrees with the season in which the proposed year falls. Then under the golden number in the lower row of the table the epact of the chosen year cvan be found, or at least the symbol "*". Thus, when the epact or the * has been found in the calendar, that day will be the new moon. The golden number will be found in the prior canon or from a table of epacts in agreement with the chosen season, by assigning the first golden number of that table to the that year from which the usage of the table starts, the second golden number to the following year, etc. In this way the epact can be found without the golden number, if the first epact of the table is assigned to that year from which the usag of the table starts, the second epact to the following year, etc.

For example: The golden number in 1582--the year of correction--is 6, which of course is the first in the first table, use of which begins on October 15th of the aforementioned year 1582 with ten days previously subtracted. So then the epact is XXVI, which lies below the golden number 6, and the new moon will fall on October 27th, and November 26th, and December 25th. Likewise in the now-corrected year 1583 the golden number is 7, under which in the same table epact VII has been placed, which will indicate the new moons for that entire year in the calendar: So in January 24th, February 22, March 24th, etc.

{ANOTHER Table of Epacts Corresponding to Golden Numbers from 1700 Inclusive to 1900 Exclusive}

{ANOTHER Table of Epacts Corresponding to Golden Numbers from 1900 Inclusive to 2200 Exclusive}

To eliminate doubt about the usage of this new table of epacts, let's demonstrate for the sake of example. In 1901, X should be the epact, which lies below the golden number 2; then a new moon will fall on January 21st, February 19th, March 21st. In the same way the epact in 1902 should be XXI which lies below golden number 3 and which will show on the calendar the new moons throughout the year. So in January on the 10th, in February on the 8th, in March on the tenth. And so on for years proceeding in order, returning to the beginning of the table whenever it's been run thru. On the other hand in 1911 the epact is not indicated by a number by by the symbol *, which lies below golden number 12 and will indicate the new moons on the calendar for the entire year, namely in January on the 1st and 31st, in March (for there is then no new moon in February since the sign * isn't found in it) the 1st and 31st, in April on the 29th, etc.

Finally: In 1916 the golden number is 17, but under this in the row of epacts in the fourth table, which matches the chosen year, the epact 25 is found not in Roman numerals like the other epacts but written in common numerals. Whenever in the calendar for the year 1916 epact 25 is found written in common numerals, the new moon will fall there, as on January 6th, Feb. 4th, March 6th, April 4th, etc. For however many times epact 25 corresponds to golden numbers greater than 11, which are the eight later ones from 12 to 19, epact 25 written in common numerals is to be selected on the calendar; but when that same epact corresponds to one of the numbers less tha 12, which are the 11 earlier ones from 1 to 11 inclusive, epact XXV written in roman numerals is to be selected on the calendar: This affects only epact 25, never the other epacts; this is done so that the lunar years might more perfectly line up with the solar years.. On account of which two epacts--namely XXV and XXIV--are assigned to six dates in the calendar.

{TABLE of Dominical Letters from October 15th, 1582, the Correction Year (with ten days first removed) inclusive, to the year 1700 Exclusive}

Use of the table is this: To the correction year 1582 after Oct. 15th (w. the previous 10 days eliminated) the letter C of the 1st box is assigned, and in the following year 1583 B is assigned from the second box, and in 1584 let Ag be put in from the third box, and thus let all the boxes be assigned in order to all the years until one has arrived at the desired year, with a return to the start of the table whenever you run thru it all. For the box onto which the desired year falls--as long as it is before the year 1700--shall given the dominical letter for that year.

If a single letter is there, the year is common; if however a double letter, it is bissextile, and the the higher letter shows the dominical day on the calendar from the beginning of the year all the way to the feast of St. Matthew the Apostle; the lower letter shows it from this feast to the end of the year.

For example: Let's figure out the dominical letter of the year 1587. Count from 1582--which you assign to the first letter C--all the way to 1587 by marking each year one-by-one to each box (counting whenever there's a twinned letter, higher and lower, as a single box), and the year 1587 falls on the letter D, which occupies the 6th place in the table. Therefore, there is for this entire year the dominical letter D, and the year is a common one, since a single letter occurs. And again, let's figure out the dominical letter of the year 1612--returning to the start of the bale once you have run thru it all--and you arrive at the two letters Cb, put in the seven place. This year then is bissextile, since two letters occur, and the higher letter C shows the dominical day from the beginning of this year all the way to the feast of St. Matthew, the lower b applies for the remainder of the year.

{ANOTHER Table of Dominical Letters from 1901 Inclusive to 2100 Exclusive}

Use of the table is this: To the year 1901 the letter F of the 1st box is assigned, and in the following year 1902 E is assigned, and thus let all the boxes be assigned in order to all the years until one has arrived at the desired year, with a return to the start of the table whenever you run thru it all. For the box onto which the desired year falls--as long as it is before the year 1700--shall given the dominical letter for that year. If a single letter is there, the year is common; if however a double letter, it is bissextile, and the the higher letter shows the dominical day on the calendar from the beginning of the year all the way to the feast of St. Matthew the Apostle; the lower letter shows it from this feast to the end of the year.

CONCERNING THE INDICTION

The Indiction is a cycle of 15 years from 1 to 15; when one cycle is completed it returns again to 1, and from January the appropriate year of this cycle takes up the opening in papal bulls. Since there is frequent use of indictions in diplomatic and scriptural publications, we will easily discover the current year of indiction for any chosen year from the following table, whose usage is perpetual: It starts from the year of correction 1582.

{TABLE of Indiction from 1582, the Correction Year}

For if to the year 1582 you take the first number, which is 10, and to the following year 1583 you assign the second number, which is 11, and so on to the desired year--returning to the start of the table anytime you run completely thru it--the desired year will fall on the indiction which you seek.

CONCERNING MOVABLE FEASTS

Because (according to a decree of the holy Council of Nicaea) Easter, a date on which the remaining movable feasts depend, should be celebrated in the Sunday which follows next after the XIV day of the first month's moon (it is called the "first month" among the Jews if its moon falls on the day of the vernal equinox, which comes on either March 21st or properly follows it), it is enacted that if the epact of any desired year is found, and it is marked out on the calendar in the days between March 8th and April 5th inclusive (for the XIV day of the moon of this epact falls either on the day of the vernal equinox--that is on March 21st or the properly following day),14 days (inclusive) shall be enumerated downward; The next Sunday following this XIV day (let us not harmonize with the Jews, if by chance the XIV day of the moon falls on a Sunday) shall be Easter day.

Example: In the year 1605, the epact is X, and the dominical letter B. And since we find epact X for dates between Mar. 8 and Apr. 5 inclusive has been placed starting at March 21st, from this date, if 14 lines number the days downward, we should find the 14th day of the moon on the 3rd of April, which is a Sunday, since in this year the dominical letter will be b. And so that we do not agree with the Jews, who celebrate Passover on the 14th day of the moon, the dominical letter b which follows the XIV day of the moon should be taken, which is obviously located on the 10th of April: And in that year Easter will be celebrated on the 10th of April. Likewise in 1604, the epact is XXIX, and there are two dominical letters DC since that year is bissextile. If then from epact XXIX, which falls between 8 March and 5 April inclusive on April 1, 14 days are counted, the XIV day of the moon falls on 14 Apr. And because the latter dominical letter is in force, namely C, that day after 14 April--that is, the one located after the XIV day of the moon--is on April 18th, Easter will be celebrated in that year on Apr. 18th.

Moreover, so that it might be easier to find all movable feasts, the two following paschal tables have been constructed, one old, the other new. From the old table movable feasts will be found thus: In the left side of the table the current epact should be taken and the current dominical letter taken from the line of dominical letters below the current epact; Then if the current dominical letter is taken from the space of the current epact, the same dominical letter should be taken from the next lower. For from the line of this dominical letter all the movable feasts are fixed. For example: In 1606, the epact is XXI, and the dominical letter A. If then in the old table the dominical letter A which lies below epact XXI is taken, Septuagesima Sunday shall be found on this line on Jan 22, Ash Wednesday Feb 8th, Easter Mar. 26, the Lord's ascension May 4th, Pentecost May 14, and the feast of Corpus Christi May 25. There will be 28 Sundays between Pentecost and Advent, and Advent will be celebrated on Dec. 3; and so on. Likewise in 1605, the epact is X and the dominical letter B, which is found in the table outside the line for epact X. For this reason the other letter B should be taken which is found on the next-lower line, from which line you will find Septuagesima on Feb 6, Ash Wednesday Feb 23, Easter Apr 10, etc.

However is should be noted that just as in a common year, when the dominical letter falls outside the space of the epact in the old table, the same letter is taken in the next-lower epact, as we said; this occurs also in a bissextile year, if one or the other of the two dominical letters then current is found outside the epact, the next two similar letters are to be taken from the next-lower epact to find the movable feasts.

From the new Easter table the same movable feasts can be found thus: In the box of the current dominical letter the current epact is sought out. For from this directive all the movable feasts can be found. As in 1609 in the box of dominical letter D, the one then current, from the line of epact XXIV, which is current in the same year, Septuagesima is held on Feb 15, Ash Wednesday mar 4, Easter Apr 19, etc.

But whether the old or new paschal table is used, all movable feasts which come after the feast of St. Matthew the Apostle should be found via the later dominical letter in bissextile years; to be clear, each of the two letters should be taken for this or that feast needing determination, such that one day is added to Septuagesima and Ash Wednesday found in January and February. What therefore happens is that the first dominical letter is current before St. Matthew's day, which always follows the earlier in the calendar; however, after the feast of St. Matthew, in February, let the later day be current, then the intercalary day is added such that Feb 24 should be called the 25th, and the 25th the 26th, etc. But if Ash Wednesday should fall in March, nothing should be added because then the latter letter is current and the days of the month correspond to the appropriate numbers. In truth, unless they are tracked down thru the latter letter, the Septuagesima will not be found properly in a bissextile year with current epact XXIV or XXV and dominical letter DC, as would clearly happen in the second and third example for the years 4088 and 3784. For example: In the bissextile year 2096 the epact will be V and the dominical letters Ag. Therefore if the movable feast is tracked down with the latter letter, which is g, Septuagesima would fall on Feb 11 and Ash Wednesday Feb 28. If however one day is added, Septuagesima will fall on Feb 12, which is Sunday, and Ash Wednesday on Feb 29, which is a Wednesday. Easter, however and the remaining feasts will fall on those days which have been given by the table. Likewise in the bissextile 4088, the epact will be XXIV and the dominical letter Dc. If then the movable feasts are determined thru the letter c--which is the latter one---Septuagesima will be found on Feb 21 and if one day is added, it would fall on Feb 22, which is a Sunday. Ash Wednesday, however, would fall on Mar 10: for this reason nothing is added, etc. Returning to the bissextile year 3784, the epact will be XXV and the dominical letters Dc. So then thru the latter c Septuagesima is found on Feb 21; this is, with one day added, the 22nd. But if we had calculated things using the prior letter D in either of these two years, nothing would have been accomplished, since below epacts XXIV and XXV the letter d would indicate Septuagesima on Feb 15, which is incorrect, since in that year the latter letter d puts Easter on April 25, and hence Septuagesima ought to be celebrated on Feb 22, as it correctly tallys if the sundays are counted backwards from Easter to Septuagesima.

Moreover, in the front of the old, reformatted paschal table we have placed to the left of the epacts golden numbers in the same order in which they were customarily placed before the correction of the calendar, as the movable feasts used to be found using these. This has been done by us for the sole reason that Easter and the other movable feasts from the Nicaean Council all the way to 1582 could be calculated. By the same method movable feasts are calculated earlier by the golden numbers so distributed, hence forward by epacts. If it need be explored, for the sake of example, when might these feasts have been celebrated in 1450? Since in that year the golden number was 7 and the dominical letter D, if the golden number 7 is found on the left side and the first letter D occurring below it, it can be found from the line of this letter d that the Septuagesima was on Feb 1, Ash Wednesday Feb 18, Easter April 5, etc.

The Advent of the Lord is always celebrated on the Sunday which is nearer the feast of St. Andrew the Apostle, namely from Nov 27 to Dec 3 inclusive. So then the current dominical letter which is found on the calendar between Nov 27 to Dec 3 indicates Advent Sunday. So for the sake of clear expression, if the dominical letter is G, Advent Sunday falls on Dec 2, because the letter G is there in the calendar, etc.

Finally, at the end of the paschal tables has been placed a temporary table of many years, from whose lines all movable feasts may be found; indeed this table is extracted from the paschal tables, from which boundless others can be determined for any years at all.