Inter gravissimas (English: "Among the most serious...") was a papal bull issued by Pope Gregory XIII on 24 February 1582. [1] [2] The document, written in Latin, reformed the Julian calendar. The reform came to be regarded as a new calendar in its own right and came to be called the Gregorian calendar, which is used in most countries today.
The intention expressed by the text of this bull was "to restore" the calendar so that seasonal events critical for the calculation of Easter dates would be back in their "proper places" and would be prevented from being moved away again. The idea of reform as such is not otherwise mentioned. The bull identifies "three necessary" things for the correct determination of Easter dates: correct placement of the northern vernal equinox; correct identification of the "14th day of the moon" (effectively full moon) that happens on or next after the vernal equinox, and the first Sunday that follows that full moon. The first two items were the ones that received attention; the third, about choosing the next following Sunday, was not identified as causing any problem, and was not further mentioned.
By "restore", Gregory meant two things. First, he adjusted the calendar so that the vernal equinox was near March 21, where it had been during the Council of Nicaea (20 May– 25 August 325). This required removing ten days of drift. Second, he made the tabular 14th day of the moon correspond with the real full moon, removing "four days and more" of drift. This would restore the dates of Easter to near where they were at the time of the Council of Nicaea, although that council had not specified where in the calendar the vernal equinox should fall and had not adopted any particular type of lunar tables. The practices of the Roman Catholic Church that had become traditional by 1582 for calculating the Easter and lunar calendars became settled when Dionysius Exiguus translated the rules of the Church of Alexandria from Greek into Latin in 525. (Northumbria adopted them at Whitby in 664, the Welsh around 768, and France around 775. Before this, France and Rome had used Victorius's less exact 457 translation of the Coptic calendar; Britain and Rome before Victorius had used Augustalis's 84-year cycle.)
Gregory also made changes to the calendar rules, intending to ensure that, in the future, the equinox and the 14th day of the Paschal moon, and consequently Easter Sunday, would not move away again from what the bull called their proper places.
The changes (relative to the Julian calendar) were as follows:
The name of the bull consists of the first two words of the bull, which starts: "Inter gravissimas pastoralis officii nostri curas…" ("Among the most serious duties of our pastoral office…").
The bull refers to "the explanation of our calendar" and to a canon related to the dominical letter. To accompany the bull there were six chapters of explanatory rules ('canons'), [3] and some of these (canons 1, 2, 4) refer to a book entitled Liber novæ rationis restituendi calendarii Romani [4] for a fuller explanation of the tables than that contained in the canons (or the bull). Because the bull and canons refer to each other, they must have been written at roughly the same time, printed at the same time (1 March), and distributed to the several countries together.
These canons enabled the computation of Easter dates in the reformed ('restored') Gregorian calendar, and gave two calendar-listings saints' days, one for the 'year of correction' (1582) and another for the entire new Gregorian year. The bull, canons, and calendars were reprinted as part of the principal book explaining and defending the Gregorian calendar, Christoph Clavius, Romani calendarii a Gregorio XIII. P. M. restituti explicatio (1603), [5] which is tome V in his collected works Opera Mathematica (1612). [6]
The version of "Inter gravissimas" included by Christoph Clavius in his work explaining the Gregorian calendar contained these dating clauses: "Anno Incarnationis Dominicae M. D. LXXXI. Sexto Calend. Martij, Pontificatus nostri Anno Decimo. ... Anno à Natiuitate Domini nostri Iesu Christi Millesimo Quingentesimo Octuagesimo secundo Indictione decima,". [5] These clauses include four years:
All of these years agree that the bull was dated 24 February 1582, using the modern 1 January beginning of the year.
 |
Gregory's reform was enacted in the most solemn of forms available to the Church, but the bull had no authority beyond the Catholic Church and the Papal States. The changes which Gregory was proposing included changes to the civil calendar over which Gregory had no authority (except in the Papal States). The text of the bull recognized this by giving what amounted to orders to the clergy and those "presiding over churches": but in contrast, where the text addresses the civil authorities ("kings, princes and republics"), it "asks", "exhorts" and "recommends" the new calendar changes. The changes required adoption by the civil authorities in each country to have legal effect.
The bull Inter gravissimas was immediately adopted by the major Catholic powers of Europe, but the Protestant countries refused to adopt it until the 18th century, and Eastern European countries adopted it only during or after World War I (the last European country to adopt it was Greece, in 1923).
Most Eastern Orthodox Churches and Oriental Orthodox Churches have not adopted it at all and continue to reckon their ecclesiastical years by the Julian calendar, even though their home countries use the Gregorian calendar for civil purposes.
Easter, also called Pascha or Resurrection Sunday, is a Christian festival and cultural holiday commemorating the resurrection of Jesus from the dead, described in the New Testament as having occurred on the third day of his burial following his crucifixion by the Romans at Calvary c. 30 AD. It is the culmination of the Passion of Jesus Christ, preceded by Lent, a 40-day period of fasting, prayer, and penance.
The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year. The Julian calendar is still used as a religious calendar in parts of the Eastern Orthodox Church and in parts of Oriental Orthodoxy as well as by the Amazigh people.
Pope Gregory XIII, born Ugo Boncompagni, was head of the Catholic Church and ruler of the Papal States from 13 May 1572 to his death in April 1585. He is best known for commissioning and being the namesake for the Gregorian calendar, which remains the internationally accepted civil calendar to this day.
The Revised Julian calendar, or less formally the new calendar and also known as the Milanković calendar, is a calendar proposed in 1923 by the Serbian scientist Milutin Milanković as a more accurate alternative to both Julian and Gregorian calendars. At the time, the Julian calendar was still in use by all of the Eastern Orthodox Church and affiliated nations, while the Catholic and Protestant nations were using the Gregorian calendar. Thus, Milanković's aim was to discontinue the divergence between the naming of dates in Eastern and Western churches and nations. It was intended to replace the Julian calendar in Eastern Orthodox Churches and nations. From 1 March 1600 through 28 February 2800, the Revised Julian calendar aligns its dates with the Gregorian calendar, which had been proclaimed in 1582 by Pope Gregory XIII.
Reform of the date of Easter refers to proposals to change the date for the annual celebration of Easter. These proposals include setting a fixed date or agreeing between Eastern and Western Christendom a common basis for calculating the date of Easter so that all Christians celebrate the Festival on the same day. As of 2023, no such agreement has been reached.
Aloysius Lilius, also variously referred to as Luigi Lilio or Luigi Giglio, was an Italian physician, astronomer, philosopher and chronologist, and also the "primary author" who provided the proposal that became the basis of the Gregorian Calendar reform of 1582.
The Coptic calendar, also called the Alexandrian calendar, is a liturgical calendar used by the Coptic Orthodox Church and also used by the farming populace in Egypt. It was used for fiscal purposes in Egypt until the adoption of the Gregorian calendar on 11 September 1875. This calendar is based on the ancient Egyptian calendar. To avoid the calendar creep of the latter, a reform of the ancient Egyptian calendar was introduced at the time of Ptolemy III which consisted of adding an extra day every fourth year. However, this reform was opposed by the Egyptian priests, and the reform was not adopted until 25 BC, when the Roman Emperor Augustus imposed the Decree upon Egypt as its official calendar. To distinguish it from the Ancient Egyptian calendar, which remained in use by some astronomers until medieval times, this reformed calendar is known as the Coptic or Alexandrian calendar. Its years and months coincide with those of the Ethiopian calendar but have different numbers and names.
As a moveable feast, the date of Easter is determined in each year through a calculation known as computus. Easter is celebrated on the first Sunday after the Paschal full moon. Determining this date in advance requires a correlation between the lunar months and the solar year, while also accounting for the month, date, and weekday of the Julian or Gregorian calendar. The complexity of the algorithm arises because of the desire to associate the date of Easter with the date of the Jewish feast of Passover which, Christians believe, is when Jesus was crucified.
The Swedish calendar or Swedish style was a calendar in use in Sweden and its possessions from 1 March 1700 until 30 February 1712. It was one day ahead of the Julian calendar and ten days behind the Gregorian calendar. Easter was calculated astronomically, with a minor exception, from 1740 to 1844.
The epact used to be described by medieval computists as the age of a phase of the Moon in days on 22 March; in the newer Gregorian calendar, however, the epact is reckoned as the age of the ecclesiastical moon on 1 January. Its principal use is in determining the date of Easter by computistical methods. It varies from year to year, because of the difference between the solar year of 365–366 days and the lunar year of 354–355 days.
Calendar reform or calendrical reform is any significant revision of a calendar system. The term sometimes is used instead for a proposal to switch to a different calendar design.
Christopher Clavius, was a Jesuit German mathematician, head of mathematicians at the Collegio Romano, and astronomer who was a member of the Vatican commission that accepted the proposed calendar invented by Aloysius Lilius, that is known as the Gregorian calendar. Clavius would later write defences and an explanation of the reformed calendar, including an emphatic acknowledgement of Lilius' work. In his last years he was probably the most respected astronomer in Europe and his textbooks were used for astronomical education for over fifty years in and even out of Europe.
Birkat Hachama refers to a rare Jewish blessing that is recited to the Creator, thanking God for creating the sun. The blessing is recited when the Sun completes its cycle every 28 years on a Tuesday at sundown. Jewish tradition says that when the Sun completes this cycle, it has returned to its position when the world was created. Because the blessing needs to be said when the Sun is visible, the blessing is postponed to the following day, on Wednesday morning.
The March equinox or northward equinox is the equinox on the Earth when the subsolar point appears to leave the Southern Hemisphere and cross the celestial equator, heading northward as seen from Earth. The March equinox is known as the vernal equinox in the Northern Hemisphere and as the autumnal equinox in the Southern Hemisphere.
The controversy over the correct date for Easter began in Early Christianity as early as the 2nd century AD. Discussion and disagreement over the best method of computing the date of Easter Sunday has been ongoing ever since and remains unresolved. Different Christian denominations continue to celebrate Easter on different dates, with Eastern and Western Christian churches being a notable example.
The Calendar Act 1750, also known as Chesterfield's Act or the British Calendar Act of 1751, is an Act of the Parliament of Great Britain. Its purpose was for Great Britain and the British Empire to adopt the Gregorian calendar. The Act also changed the start of the legal year from 25 March to 1 January.
An ecclesiastical full moon is formally the 14th day of the ecclesiastical lunar month in an ecclesiastical lunar calendar. The ecclesiastical lunar calendar spans the year with lunar months of 30 and 29 days which are intended to approximate the observed phases of the Moon. Since a true synodic month has a length that can vary from about 29.27 to 29.83 days, the moment of astronomical opposition tends to be roughly 14.75 days after the previous conjunction of the Sun and Moon. The ecclesiastical full moons of the Gregorian lunar calendar tend to agree with the dates of astronomical opposition, referred to a day beginning at midnight at 0 degrees longitude, to within a day or so. However, the astronomical opposition happens at a single moment for the entire Earth: The hour and day at which the opposition is measured as having taken place will vary with longitude. In the ecclesiastical calendar, the 14th day of the lunar month, reckoned in local time, is considered the day of the full moon at each longitude.
The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull Inter gravissimas issued by Pope Gregory XIII, which introduced it as a modification of, and replacement for, the Julian calendar. The principal change was to space leap years differently so as to make the average calendar year 365.2425 days long, more closely approximating the 365.2422-day 'tropical' or 'solar' year that is determined by the Earth's revolution around the Sun.
The year 1582 in science and technology included a number of events, some of which are listed here. This year sees the introduction of the Gregorian calendar, promulgated by Pope Gregory XIII in the Papal bull Inter gravissimas on February 24 and based largely on the work of Christopher Clavius. Under the Habsburg monarchy in Spain, Portugal and Italy, together with the Polish–Lithuanian Commonwealth, the year continues under the Julian calendar as normal until Thursday October 4, the next day becoming Friday October 15; France follows two months later, letting Sunday December 9 be followed by Monday December 20. Other countries switch in later years.
The adoption of the Gregorian Calendar has taken place in the history of most cultures and societies around the world, marking a change from one of various traditional dating systems to the contemporary system – the Gregorian calendar – which is widely used around the world today. Some states adopted the new calendar in 1582, others not before the early twentieth century, and others at various dates between. A few have yet to do so, but except for these, the Gregorian calendar is now the world's universal civil calendar, old style calendars remaining in use in religious or traditional contexts. During – and for some time after – the transition between systems, it has been common to use the terms "Old Style" and "New Style" when giving dates, to indicate which calendar was used to reckon them.