n.

1. Any of various systems of reckoning time in which the beginning, length, and divisions of a year are defined.
2. A table showing the months, weeks, and days in at least one specific year.
3. A schedule of events.
4. An ordered list of matters to be considered: a calendar of court cases; the bills on a legislative calendar.
5. Chiefly British. A catalog of a university.

tr.v., -dared, -dar·ing, -dars.

To enter in a calendar; schedule.

[Middle English calender, from Old French calendier, from Late Latin kalendārium, from Latin, account book, from kalendae, calends (from the fact that monthly interest was due on the calends).]

A system that gives a name to each day. Ancient calendars were based on observations of phenomena such as the waxing and waning of the Moon, the change in seasons, or the movement of heavenly bodies. Modern calendars tend to be based solely on arithmetical rules, distanced from their motivation in nature.

Most calendars divide a year into an integral number of months and divide months into an integral number of days. However, these astronomical periods—day, month, and year—are incommensurate, so exactly how these time periods are coordinated and the accuracy with which they approximate their astronomical values are what differentiate one calendar from another. See also Day; Earth rotation and orbital motion; Month; Year.

Dozens of calendars are still in use, in addition to the almost universally used Gregorian calendar. Many religious holidays and national events are determined by dates on these calendars. Solar calendars—including the Egyptian, Julian, Coptic, Ethiopic, Gregorian, and Persian—are based on the yearly solar cycle, whereas lunar calendars such as the Islamic and lunisolar calendars such as the Hebrew, Hindu, and Chinese take the monthly lunar cycle as the basic building block. Most solar calendars are divided into months, but these months are divorced from the lunar events; they are sometimes related to the movement of the Sun through the twelve signs of the zodiac.

Almost every calendar incorporates a notion of “leap” year to correct the cumulative error caused by approximating a year by an integral number of days and months. Solar calendars add a day every few years to keep up with the astronomical year.

The simplest naming convention would be to assign an integer to each day; fixing day 1 would determine the whole calendar. The Babylonians had such a day count, as did the Maya and the Hindus. Astronomers, especially those studying variable stars, use Julian day numbers to specify dates. The Julian period, introduced in 1583 by Joseph Justus Scaliger, was originally a counting of years in a cycle of 7980 years, starting from 4713 B.C.E. (before the common era; or B.C.); nineteenth-century astronomers adapted the system into a strict counting of days backward and forward from JD0 = noon on Monday, January 1, 4713 B.C.E. (Julian) = noon on Monday, November 24, −4713 (Gregorian). A fractional part of a Julian day gives the fraction of a day beyond noon. Computer scientists often use diurnal calendars as an intermediate device for converting from one calendar to another.

The Gregorian calendar, now in common use throughout the world, is based on a 12-month year that closely approximates the Earth's solar cycle. This calendar was designed by a commission assembled by Pope Gregory XIII in the sixteenth century; the main author of the new system was the Naples astronomer Aloysius Lilius. This calendar is based on a 365-day common year divided into 12 months, and on 366 days in leap years, the extra day being added to the second month. A year is a leap year if it is divisible by 4 and is not a century year (multiple of 100) or if it is divisible by 400. For example, 1900 is not a leap year; 2000 is a leap year. The Gregorian calendar differs from its predecessor, the Julian calendar, only in that the Julian calendar did not include the century rule for leap years—all century years were leap years.

Since every fourth year on the Julian calendar was a leap year, a cycle of 4 years contained (4 × 365) + 1 = 1461 days, giving an average length of year of 365.25 days. This is somewhat more than the mean length of the tropical year, and over the centuries the calendar slipped with respect to the seasons. By the sixteenth century, the date of the spring equinox had shifted from around March 21 to around March 11. Pope Gregory XIII instituted only a minor change in the calendar: century years not divisible by 400 would no longer be leap years. (He also improved the rules for Easter.) Thus, three out of four century years are common years, giving a cycle of 400 years containing (400 × 365) + 97 = 146,097 days and an average year length of 146,097/400 = 365.2425 days. He also corrected the accumulated 10-day error in the calendar by proclaiming that Thursday, October 4, 1582 C.E., the last date in the old-style (Julian) calendar, would be followed by Friday, October 15, 1582, the first day of the new-style (Gregorian) calendar. Catholic countries followed his rule, but Protestant countries resisted. Turkey did not switch to the Gregorian calendar until 1927.

The Islamic calendar is an example of a strictly lunar calendar, with no intercalation of months (unlike lunisolar calendars). Its independence of the solar cycle means that its months do not occur in fixed seasons but migrate through the solar year.

Lunisolar calendars invariably alternate 12- and 13-month years. The so-called Metonic cycle is based on the observation that 19 solar years contain almost exactly 235 lunar months. This correspondence, named after the Athenian astronomer Meton and known much earlier to ancient Babylonian and Chinese astronomers, makes a relatively simple and accurate fixed solar/lunar calendar feasible. The 235 = (12 × 12) + (7 × 13) months in the cycle are divided into 12 years of 12 months and 7 leap years of 13 months. The 7 leap years are evenly distributed within the 19-year cycle, with gaps of 1 or 2 years between them. The Metonic cycle is (currently) accurate to within 6.5 minutes a year and is still employed in the Hebrew calendar (instituted in 359 C.E.) and for the ecclesiastical calculation of Easter.

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Schedule of upcoming securities that will be brought to market. For example, the weekly auctions of U.S. Treasury securities, municipal bonds offered for sale, and also Asset-Backed Securities offered for sale by banks and investment banks.

noun

An organized list, as of procedures, activities, or events: agenda, docket, lineup, order of the day (often used in plural), program, schedule, timetable. See planned/unplanned.

time A scheme for grouping, labelling, and thereby distinguishing the individual days. The Moon and the Sun provide conspicuous natural groupings of very suitable size: the former the lunar period or month of about 30 days, the latter the solar period or year of about 365 days, i.e. about 12 of the lunar periods. (As discussed under month and year, these periods exist in several forms; here we are concerned with the obvious period for each, explicitly the synodic month and the tropical year. The week as an entity is essentially artificial, not necessarily of seven days, and of peripheral interest in this context.) Unfortunately, neither grouping is an exact number of days, nor is the year an exact multiple of the natural month. While the familiar calendar adheres closely to the natural year, by incorporating months of relatively arbitrary size, the Jewish and Moslem calendars, for instance, have a natural month but a more erratic year. History has seen a great variety of renderings for these incompatibilities.

The lengths of the average natural (synodic) month and (tropical) year, in terms of the average natural (mean solar) day, are as follows:

1 month	= 29.530 59~ days
1 year	= 365.242 22~ days

hence

1 year

= 12.368 27~ months.

With the recurrent pattern of the seasons of more functional significance than that of the Moon, there is an obvious advantage in giving primacy to fitting with the natural year. Since any reasonable calendar will be built on whole days, the fractional 0.242 2~ must be accommodated carefully if the calendar is to stay in step with the seasons. This, of course, is the cause of the leap year being in the familiar calendar. Introduced by Julius Caesar in the year 45 BCE by adding an extra day to February (the last full month of the year, which started at the spring equinox) every fourth year, this extra day (an intercalary day) equated the year with 365.25 days, and hence overstated the need by about one day every 128 years. Thus, with this Julian calendar, the average period for the year exceeded that of the seasons, so they came progressively earlier as the centuries passed. By the 16th century this amounted to about 13 days. While the perturbation within a lifetime was insignificant, and the placement of equinoxes and solstices did not have naturally compelling points in the calendar, it was decided at that time both to alter the pattern so as to approximate yet more closely the true natural year and to reset the calendar to put the seasonal markers close to their traditional points in the calendar. Thus, Pope Gregory XIII adopted for the Roman Catholic Church what is known as the Gregorian calendar, with leap years not occurring in years that were multiples of 100 unless they were multiples of 400. Thus excluding three days per 400 years, this equated the year with 365 ⁹⁷/₄₀₀ = 364.242 5~ days - still overstated but only by about one day every 3 323 years. The finer adjustment, proposed but yet to apply, and potentially to be varied because of the minutely changing length of the average day and average year, is to exclude from being leap years those years that are multiples of 4 000. This would leave the year overstated by about one day per 20 000 years.

The occurrence of the northern spring equinox on or about 21 March is thus a deliberate feature of the Gregorian calendar, harking back to the Julian, but the original cause of any such arrangement is unclear. Since the tropical year equals 365.242 2~ days, equal seasons would be of 91.31~ days. However, because Earth's orbit is elliptical and the Sun at a focus thereof rather than the geometrical centre, the four seasons routinely differ in length from one another by a few days. The northern spring is nearly 93 days and its summer nearer to 94, but the southern spring is under 90 days and its summer under 89 (but includes the time of greatest proximity to the Sun, the perihelion). Hence, while the March equinox and the June solstice tend to be on the 20th or 21st of their month, the December solstice is more often on the 22nd and the September equinox on the 23rd (the offset being less than it might be because of the pattern of month sizes tending to correspond with the astronomical pattern). (Despite the summer solstice commonly being called ‘Midsummer Day’, the practice in many countries is to regard these dates as the starts of the respective seasons rather than their midpoints. This reflects the delayed effect of the seasonal travels of the Sun, but exaggerated. The Australian practice of regarding seasons as starting with the relevant month, e.g. 1 March instead of 21 March, is much more appropriate.)

This new (and still extant) calendar was implemented by the Roman church in October 1582, with the dates 5 to 14 October that year omitted, bringing the seasonal pattern not to the conditions of Caesar's time but to those of 325 CE, the time of the Council of Nicaea. The day following 4 October 1582 ‘old style’ was thus 15 October 1582 ‘new style’. Though quickly adopted in many Catholic European countries, it was not widespread in Europe until 1700, when the continental Protestant areas adopted it, as did Scotland. England and her overseas possessions delayed introduction for 170 years, by then having to omit 11 days, jumping from 2 September 1752 ‘old style’ to 14 September 1752 ‘new style’. The Orthodox world (Russia, Greece, etc., and Turkey) waited until after World War I, by which time the correction became 13 days, a change still not accepted by the Orthodox Church, which remains Julian.

As day, month, and year are all changing in size progressively, mainly due to the tidal effects induced by extra-terrestrial gravity, the precise challenge of the calendar will change significantly in due course.

As applied to medieval manuscripts, a list of the principal feast days of the Church and the commemorative feasts of the saints throughout the liturgical year. It was an essential part of books used to celebrate Mass (the MISSAL, Pontifical and Benedictional) and the Divine Office (the PSALTER and BREVIARY), as well as of books of prayers used for private devotion (e.g. BOOK OF HOURS). Major Church feasts (e.g. Christmas and Easter), the commemorative days of the Apostles and other major saints or the names of saints particularly important in the diocese for which the book was made might be highlighted by being written in red, gold or blue. The text usually begins with an embellished KL (for Kalends, the Latin name for the first day of the month); the days of the week are indicated by lower-case letters a-g, accompanied by abbreviations of Ides and Nones. Golden numbers (i-xix) might also appear in the left column for calculating the date of the Paschal moon. Normally the text for such a calendar, with a line allocated to each day, occupied the recto and verso of 12 folios.

See the Abbreviations for further details.

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calendar

Calendar of the principal feasts of saints in this volume who are or were venerated on these days

January
1 B.V.M., Odilo, Joseph Tomasi, Zdislava Berka.
2 Basil and Gregory of Nazianzus, Munchin, Seraphim of Sarov.
3 Genevieve.
4 Roger of Ellant, Elizabeth Seton.
5 John of Nepomuk, John Neumann, Simeon Stylites.
6 Peter of Canterbury.
7 Brannoc, Kentigerna, Lucian, Raymund of Pennafort, Canute Lavard.
8 Nathalan, Pega, Wulsin, Gudule, Thorfinn, Apollinaris the Apologist.
9 Berhtwald (1).
10 Dermot, Paul the Hermit, Saethrith.
11 Paulinus of Aquileia.
12 Ailred, Benedict Biscop, Marguerite Bourgeoys, Salvius, Antony Pucci.
13 Hilary, Kentigern, Antony Pucci, Berno of Cluny.
14 Felix of Nola, Macrina the Elder, Sava of Serbia.
15 Ceolwulf, Efisio, Ita, Macarius.
16 Fursey, Henry of Coquet Island, Marcellus, Sigebert, Honoratus of Arles.
17 Antony of Egypt, Mildgyth, Sulpicius.
18 Prisca, Margaret of Hungary, Ulfrid.
19 Branwalader, Henry of Finland, Wulfstan.
20 Fabian and Sebastian, Fechin, Eustochium Calafato.
21 Agnes, Meinrad.
22 Berhtwald (2), Vincent of Saragossa, Anastasius, Vincent Pallotti.
23 Emerentiana, John the Almsgiver, Ildephonsus.
24 Babylas, Cadoc (2), Francis of Sales.
25 Dwyn, Paul, Praejectus.
26 Alberic, Bathild, Conan, Paula, Timothy and Titus, Tortgith, Augustine of Trondheim.
27 Angela, Devota, Julian of Le Mans.
28 John the Sage, Thomas Aquinas, Peter Nolasco.
29 Gildas, Julian the Hospitaller.
30
31 John Bosco, Maedoc of Ferns.

February
1 Brigid of Ireland, Cecilius, Sigebert (2), Seiriol.
2 B.V.M., Jeanne de Lestonnac, Catherine dei Ricci, Theophane Ve´nard.
3 Anskar, Blaise, Ia, Laurence of Canterbury, Margaret of England, Wereburga.
4 Andrew Corsini, Gilbert of Sempringham, Phileas, John de Britto.
5 Agatha.
6 Amand, Dorothy, Mel, Paul Miki, Vedast.
7 Richard, Romuald, Ronan (2b).
8 Cuthman, Elfleda, Jerome Emiliani, Kew, Stephen of Muret.
9 Apollonia, Teilo, Miguel Cordero.
10 Scholastica, Trumwine, William of Malavalla.
11 Caedmon, Gobnet, Gregory II, Benedict of Aniane.
12 Ethilwald (1).
13 Ermingild, Huna, Modomnoc.
14 Conran, Cyril and Methodius, Valentine, Zeno of Rome, Sava of Serbia, John Baptist of the Conception.
15 Sigfrid (2), Claude de la Colombie`re.
16 Juliana, Benedict Joseph Labre.
17 Finan of Lindisfarne, Fintan of Clonenagh, Seven Servite Founders, Martyrs of China.
18 Colman of Lindisfarne, Fra Angelico, Angilbert.
19 Conrad Confalonieri, Quodvultdeus.
20 Wulfric.
21 Peter Damian, Fructuosus.
22 Margaret of Cortona.
23 Jurmin, Milburga, Polycarp, Willigis.
24 Matthias.
25 Ethelbert of Kent, Walburga.
26
27 Alnoth, Leander, Herefrith, Gabriel Possenti.
28 Herefrith, Oswald of Worcester.
29 Cassian.

March
1 David of Wales, Swithbert, Rudesind.
2 Chad, Joavan.
3 Non, Winwaloe, Cunegund, Marinus, Katherine Drexel.
4 Adrian of May, Casimir, Owin.
5 Ciaran of Saighir, Piran, John Joseph of the Cross.
6 Baldred and Billfrith, Chrodegang, Cyneburg (1), Fridolin, Tibba, Conon, Colette, Agnes of Bohemia.
7 Eosterwine, Perpetua and Felicitas.
8 Duthac, Felix of Dunwich, John of God, Senan.
9 Pacian of Barcelona, Bosa, Constantine, Forty Martyrs of Sebaste, Frances of Rome, Gregory of Nyssa, Dominic Savio, Catherine of Bologna.
10 Kessog, John Ogilvie.
11 Oengus, Eulogius of Cordoba.
12 Alphege (2), Gregory, Mura, Paul Aurelian, Pionius.
13 Gerald of Mayo, Mochoemoc.
14
15 Longinus, Louise de Marillac, Zacharias, Clement Hofbauer.
16 Finan Lobur, Abraham Kidunaia.
17 Patrick, Withburga, Gertrude of Nivelles, John Sarkander.
18 Christian, Cyril of Jerusalem, Edward the Martyr, Finan of Aberdeen.
19 Alcmund, Joseph.
20 Cuthbert, Herbert of Derwentwater, Wulfram, Martin of Braga.
21 Benedict, Enda, Nicholas of Flue.
22
23 Gwinear, Turibius, Joseph Oriol.
24 Dunchad, Hildelith, Macartan, Catherine of Sweden.
25 B.V.M., Alfwold, Dismas.
26 Braulio, Liudger, William of Norwich.
27 Rupert.
28 Alkelda of Middleham.
29 Gwynllyw and Gwladys.
30 John Climacus, Osburga, Zosimus of Syracuse, Leonard Murialdo.
31

April
1 Agilbert, Gilbert of Caithness, Tewdric, Walaric, Hugh of Grenoble, Mary of Egypt.
2 Francis of Paola.
3 Pancras of Taormina, Richard of Chichester, Agape, Irene, and Chione.
4 Ambrose, Isidore.
5 Derfel, Vincent Ferrer, Maria Crescentia Hoss.
6 Elstan, Irenaeus of Sirmium.
7 Celsus, Finan Cam, Goran, John Baptist de La Salle.
8
9 Madrun, Mary of Egypt.
10 Beocca and Hethor, Hedda of Peterborough.
11 Gemma Galgani, Guthlac, Stanislas.
12 Zeno of Verona, Teresa of Los Andes.
13 Guinoch, Martin I, Carpus, Papylus, and Agathonice.
14 Caradoc, Tiburtius and Companions, Benezet, Bernard of Tiron.
15 Paternus of Wales, Ruadhan.
16 Bernadette, Magnus, Paternus of Avranches, Benedict Joseph Labre.
17 Donnan.
18 Laserian, Apollonius.
19 Alphege (1), Leo IX.
20 Caedwalla, Agnes of Montepulciano.
21 Anselm, Beuno, Ethilwald (2), Maelrubba.
22 Theodore of Sykeon.
23 George, Adalbert of Prague.
24 Egbert, Fidelis, Ives, Mellitus, Marie-Euphrasie Pelletier, Wilfrid.
25 Mark.
26 Cletus, Riquier.
27 Machalus, Zita.
28 Louis de Montfort, Vitalis, Peter Chanel.
29 Catherine of Siena, Endellion, Hugh of Cluny, Peter the Martyr, Robert of Molesme, Wilfrid II.
30 Erkenwald, Joseph Cottolengo, Pius V.

May
1 Asaph, Brioc, Corentin, Joseph, Marcoul, Philip and James.
2 Athanasius, Gennys, Mafalda, Nicholas Hermansson, Theodosius.
3 Conleth, Glywys, Philip and James, Pellegrino Laziosi.
4
5 Hydroc.
6 Edbert, Marian and James.
7 John of Beverley, Lindhard.
8 Indract, Odger, Victor (2), Wiro, Peter of Tarentaise.
9 Pachomius.
10 Catald, Gordian and Epimachus, Antoninus, John of Avila.
11 Comgall, Credan (1), Tudy, Maieul, Ignatius of Laconi.
12 Ethelhard, Fremund, Nereus and Achilleus, Pancras of Rome.
13 Robert Bellarmine.
14 Hallvard, Matthias, Maria Mazzarello.
15 Berchtun, Euphrasius, Isidore the Farmer.
16 Brendan the Navigator, Carantoc, Peregrine of Auxerre, Simon Stock.
17 Madron, Paschal Baylon.
18 Elgiva, Eric, John I.
19 Crispin of Viterbo, Dunstan, Peter Celestine, Pudentiana, Ivo.
20 Bernardino of Siena, Ethelbert of East Anglia.
21 Collen, Godric, Andrew Bobola, Charles de Mazenod.
22 Helen of Carnavon, Hemming, Rita of Cascia.
23 William of Rochester, Montanus and Lucius, Alexander Nevski, John Baptist Rossi.
24 David of Scotland, Vincent of Lerins.
25 Madeleine Barat, Gregory VII, Urban, Zenobius, Christopher Magallanes.
26 Augustine of Canterbury, Mariana Paredes, Philip Neri, Priscus.
27 Bede, Julius the Veteran, Melangell.
28 Bernard of Aosta, Germanus of Paris, Gizur, Lanfranc.
29 Alexander (1), M. Mag. de' Pazzi.
30 Dympna, Hubert, Joan of Arc, Ferdinand.
31 B.V.M., Petronilla.

June
1 Gwen of Brittany, Justin, Nicomedes, Ronan (2a), Whyte, Wistan.
2 Erasmus, Marcellinus and Peter, Martyrs of Lyons, Oda.
3 Clotilde, Genesius of Clermont, Kevin, Charles Lwanga and Companions.
4 Edfrith Ninnoc, Petroc, Francis Caracciolo.
5 Boniface.
6 Gudwal, Jarlath, Norbert, Primus and Felician.
7 Meriasek, Robert of Newminster, Antonio Gianelli.
8 Medard, William of York.
9 Columba, Ephraem.
10 Ithamar.
11 Barnabas, Paula Frassinetti, Mary Rose.
12 Basilides, Eskil, Leo II, Odulf, John of Sahagun, Caspar Bertoni.
13 Antony of Padua, Eulogius of Alexandria.
14 Dogmael.
15 Trillo, Vitus and Companions, Germaine Cousin.
16 Benno, Cyricus, Ismael, Lutgardis.
17 Adulf, Alban, Botulf, Briavel, Moling, Nectan, Rainier of Pisa.
18 Mark and Marcellian, Gregory Barbarigo.
19 Gervase and Protase, Juliana Falconieri, Romuald.
20 Alban, Edward the Martyr, Govan, Adalbert.
21 Aloysius Gonzaga, Leufred, Mewan.
22 Acacius, John Fisher and Thomas More, Paulinus of Nola.
23 Cyneburg, Etheldreda, Joseph Cafasso.
24 Bartholomew of Farne, John the Baptist.
25 Adalbert, William of Montevergine, Maximus of Turin, Prosper.
26 John and Paul, Salvius.
27 Cyril of Alexandria, Zoilus.
28 Austell, Irenaeus, Potamiaena and Basilides.
29 Elwin, Judith and Salome, Peter and Paul.
30 Martyrs of Rome, Theobald of Provins, George the Hagiorite.

July
1 Julius and Aaron, Oliver Plunket, Serf.
2 B.V.M., Processus and Martinian, Oudoceus, John Francis Regis, Bernardino Realino.
3 Germanus of Man, Thomas, Raymund Gayrard.
4 Elizabeth of Portugal, Andrew of Crete, Ulric (1).
5 Modwenna, Morwenna, Antony Zaccaria, Athanasius the Athonite.
6 Maria Goretti, Monenna, Newlyn, Sexburga, Godeliva.
7 Boisil, Erkengota, Ethelburga (2), Hedda of Winchester, Maelruain, Merryn, Palladius, Thomas of Canterbury, Willibald, Sunniva.
8 Grimbald, Kilian, Urith.
9 Everild, Veronica Giuliani, Martyrs of Gorkum.
10 Alexander (2), Canute, Seven Brothers.
11 Benedict, Drostan, Thurketyl, Olga.
12 John Gualbert.
13 Henry the Emperor, Mildred, Silas.
14 Boniface of Savoy, Camillus, Deusdedit, Phocas of Sinope, Francis Solano.
15 Bonaventure, David of Sweden, Donald, Swithun, Vladimir.
16 Helier, Plechtelm, Stephen Harding Tenenan.
17 Alexis, Kenelm, Martyrs of Scillium, Hedwig (2).
18 Arnulf (1), Edburga of Bicester, Edburga of Winchester.
19 Macrina the Younger.
20 Arild, Margaret of Antioch, Wilgefortis, Wulmar.
21 Arbogast, Laurence of Brindisi, Praxedes, Victor.
22 Mary Magdalene, Wandrille.
23 Apollinaris, Bridget of Sweden, Cassian, Apollonius, Magi.
24 Christina, Wulfhad, and Ruffin, Boris and Gleb, Lewinna.
25 Christopher, James the Great.
26 Joachim and Anne.
27 Pantaleon, Seven Sleepers, Seven Apostles of Bulgaria, Raymund Palmen'o.
28 Botvid, Samson.
29 Lupus, Martha, Olaf, Simplicius, Sulian.
30 Abdon and Sennen, Peter Chrysologus, Tatwin.
31 Germanus of Auxerre, Ignatius Loyola, Joseph of Arimathea, Neot, Justin de Jacobis, Helen of Skovde.

August
1 Aled, Alphonsus, Ethelwold, Kyned, Maccabees, Peter Julian Eymard.
2 Etheldritha, Eusebius, Plegmund, Sidwell, Stephen I, Thomas of Hales.
3 Manaccus, Waldef.
4 Molua, Sithney, John Baptist Vianney.
5 Cassyon, Oswald of Northumbria.
6 Sixtus.
7 Cajetan.
8 Dominic, Lide.
9 Romanus (1).
10 Bettelin (2), Laurence.
11 Blane, Clare, Tiburtius and Susanna.
12 Jambert, Murtagh.
13 Pontian and Hippolytus, Radegund, Wigbert, Benild, Maximus the Confessor, John Berchmans.
14 B.V.M., Arnulf (2), Maximilian Kolbe.
15 Jeanne Delanoue, Hyacinth of Cracow.
16 Armel, Roch, Stephen of Hungary, Laurence Loricatus.
17 Clare of Montefalco.
18 Agapitus, Helena.
19 Credan (2), John Eudes, Mochta, Louis of Toulouse.
20 Bernard, Oswin, Philibert, Rognvald.
21 Pius X.
22 Alexander (3), Arnulf (3), Philip Benizi, Sigfrid (1).
23 Rose of Lima, Timothy and Companions, Tydfil.
24 Bartholomew, Ouen.
25 Joseph Calasanz, Ebbe, Genesius of Arles, Louis IX, Maria Kowalska.
26 Bregwine, Fillan, Maximilian, Ninian, Pandonia, Tarsicius, Zephyrinus.
27 Decuman, Monica, Rufus, Caesarius of Arles.
28 Augustine of Hippo, Hermes, Julian of Brioude.
29 Edwold, John the Baptist, Sebbi.
30 Felix and Adauctus, Fiacre, Rumon.
31 Aidan, Cuthburga, Eanswith, Quenburga, Waldef (1), Raymund Nonnatus.

September
1 Drithelm, Giles, Priscus of Capua.
2 William of Roskilde.
3 Macanisius, Gregory.
4 Ultan, Rosalia.
5 Bertin, Laurence Giustiniani.
6
7 Evurtius, Tilbert.
8 B.V.M., Disibod, Ethelburga (3), Kinemark, Thomas of Villanova.
9 Bettelin (1), Ciaran of Clonmacnoise, Peter Claver, Gorgonius, Omer, Wulfhilda.
10 Finnian of Moville, Frithestan, Nicholas of Tolentino, Aubert of Avranches, Salvius.
11 Deiniol, Protus and Hyacinth, Patiens of Lyons, John Perboyre.
12 Ailbe.
13 John Chrysostom.
14 Albert of Jerusalem, Cornelius and Cyprian.
15 Adam of Caithness, Catherine of Genoa, Mirin.
16 Cornelius and Cyprian, Edith, Geminianus, John Macias.
17 Hildegard, Lambert, Robert Bellarmine, Francis Mary of Camporosso.
18 Joseph of Copertino.
19 Januarius, Theodore of Canterbury.
20 Eustace, Korean Martyrs.
21 Matthew.
22 Emmeranus, Laudus, Maurice.
23 Adomnan, Thecla, Pius of Pietrelcina.
24 Robert of Knaresborough, Gerard Sagredo.
25 Cadoc (1), Ceolfrith, Finbar, Firmin, Florence, Sergius, Vincent Strambi, Wivina.
26 Cosmas and Damian, Cyprian and Justina, Nilus, Teresa Couderc.
27 Barry, Florentius, Vincent de Paul.
28 Lioba, Machan, Wenceslas, Faustus of Riez.
29 Michael and All Angels.
30 Honorius, Jerome, Tancred, Torthred and Tova, Gregory the Enlightener, Simon of Crepy.

October
1 Bavo, Mylor, Remigius, Theresa of Lisieux, Nicetius of Trier.
2 Guardian Angels, Leger, Thomas of Hereford.
3 Hewalds.
4 Francis of Assisi.
5 Maurus and Placid.
6 Bruno, Faith.
7 Helen of Cornwall, Osith, Justina of Padua.
8 Demetrius, Iwi, Keyne, Triduana, Pelagia.
9 Denys, John Leonardi, Luis Bertran, Martyrs of the Spanish Civil War.
10 Cassius and Florence, Francis Borgia, Geron, Paulinus of York.
11 Canice, Ethelburga (1), Loman, Alexander Sauli.
12 Edwin, Wilfrid, Meinhard.
13 Comgan, Edward the Confessor, Gerald of Aurillac.
14 Burchard, Callistus, Donatian, Manacca, Selevan.
15 Albert, Tecla, Theresa of Avila.
16 Gall, Hedwig, Lul, Gerard Majella, Anastasius.
17 Margaret-Mary Alacoque, Ethelred and Ethelbricht, Etheldreda, Ignatius of Antioch, Nothelm, Rule, John the Dwarf.
18 Gwen of Cornwall, John of Bridlington, Justus of Beauvais, Luke.
19 Jean de Bre´beuf and Isaac Jogues, Ethbin, Frideswide, Paul of the Cross, Peter of Alcantara, Ptolomaeus and Lucius.
20 Acca, Maria Boscardin, Andrew of Crete (2).
21 Fintan Munnu, Hilarion; Tuda, Ursula, Malchus, Severinus.
22 Donatus, Mellon.
23 Ethelfleda, John of Capistrano, Romanus (2), Boethius.
24 Antony Claret, Maglorius, Felix of Thibiuca.
25 Crispin and Crispinian, Forty Martyrs of England and Wales, Front of Perigueux.
26 Bean (2), Cedd, Eata.
27 Odran.
28 Simon and Jude, Salvius.
29 Colman of Kilmacduagh, Merewenna.
30 Alphonsus Rodriguez, Marcellus the Centurion, Clare of Montefalco.
31 Begu, Erc, Foillan, Quentin, Wolfgang.

November
1 All Saints, Benignus, Cadfan, Dingad, Gwythian, Vigor.
2 All Souls, Justus of Trieste.
3 Clydog, Malachy, Pirmin, Martin de Porres, Rumwold, Winefride, Wulgan.
4 Birstan, Charles Borromeo, Clether.
5 Kea, Zachary and Elizabeth.
6 Illtud, Leonard, Melaine, Mennas, Winnoc, Vietnam Martyrs.
7 Congar (2), Willibrord.
8 Cybi, Four Crowned Martyrs, Gerardin, Tysilio, Willehad.
9 Theodore.
10 Aed, Justus, Leo, Andrew Avellino.
11 Martin of Tours, Theodore the Studite.
12 Cadwaladr, Cunibert, Josaphat, Lebuin, Machar.
13 Abbo, Brice, Stanislaus Kostka, Nicholas I, Homobonus.
14 Dyfrig, Laurence O'Toole, Modan, Nicholas Tavelik.
15 Albert the Great, Fintan of Rheinau, Leopold, Malo, Raphael Kalinowski.
16 Edmund of Abingdon, Gertrude, Emilion, Margaret of Scotland, Giuseppe Moscati.
17 Gregory of Tours, Gregory the Wonder-worker, Hilda, Hugh of Lincoln, Elizabeth of Hungary, Martyrs of Paraguay, Philippine Duchesne, Acislus and Victoria, Anianus.
18 Mabyn, Mawes, Odo.
19 Ermenburga, Ronan (2c).
20 Colman of Dromore, Edmund.
21 Condedus.
22 Cecilia, Philemon and Apphia.
23 Clement, Columbanus, Alexander Nevski.
24 Chrysogonus, Colman of Cloyne, Enfleda, Minver.
25 Catherine of Alexandria.
26 Delphine, Leonard of Port Maurice.
27 Congar (1), Fergus, Virgil.
28 Juthwara, Gregory III, James of the Marches, Catherine Laboure´, Joseph Pignatelli.
29 Brendan of Birr, Francis of Lucera.
30 Andrew.

December
1 Eloi, Tudwal.
2
3 Birinus, Ethernan, Francis Xavier.
4 Barbara, John Damascene, Osmund.
5 Christina of Markyate, Justinian, Crispina, Galgano, Sabas.
6 Nicholas.
7 Ambrose, Diuma.
8 B.V.M., Budoc.
9 Leocadia, Wolfeius.
10 Eulalia.
11 Damasus, Daniel the Stylite.
12 Finnian of Clonard, Jane Chantal, Vicelin.
13 Edburga of Minster, Judoc, Lucy.
14 Fingar, Hybald, John of the Cross, Nicasius, Odile, Venantius, Fortunatus.
15 Offa of Essex.
16 Bean (1).
17 Lazarus.
18 Flannan, Mawnan, Samthann, Winnibald.
19
20 Dominic of Silos.
21 Peter Canisius, Thomas the Apostle, Beornwald.
22 Frances Cabrini.
23 Frithebert, Thorlac, Margaret d'Youville.
24 Mochua, Sharbel.
25 Alburga, Anastasia.
26 Stephen, Tathai.
27 Fabiola, John the Evangelist.
28 Holy Innocents, Gaspare del Bufalo.
29 Evroult, Thomas of Canterbury, Trophimus.
30 Egwin.
31 Sylvester.

For more information on calendar, visit Britannica.com.

The English calendar is based on that devised by Julius Caesar, the ‘Julian calendar’. It has twelve months, beginning on 1 January, but as the Christian Church disapproved of the wild festivities held by pagan Romans around that date it chose 25 March, the Feast of the Annunciation, as New Year's Day; some countries adopted this for civic purposes too, but not all. In England, the year was held to begin either on 1 January or 25 December up to the late 12th century, when 25 March was chosen instead; the two systems ran concurrently till 1751, with calendars and almanacs using 1 January, but legal and official documents using 25 March. The year reckoned in the latter way was called the ‘Year of Grace’.

Astronomically, the Julian calendar was faulty, being based on a slightly mistaken estimate of the length of a year. As centuries passed, it became visibly out of synch with the astronomical solstices and equinoxes, and in 1582 Pope Gregory XIII directed that that year be shortened by ten days, reorganized the method of reckoning leap years, and restored 1 January as New Year's Day. Catholic countries adopted this ‘Gregorian calendar’, but Protestant ones did not, though the mathematician Dr Dee argued as early as 1583 that England too should make an adjustment, preferably of eleven days. At last, in 1750, Parliament decreed that the year 1751 would end on 31 December, and that in 1752 September would be shortened by eleven days, with 2 September being followed immediately by 14 September. (The tax year, however, was not changed, and still starts on 5 April, eleven days after the old New Year date of 25 March).

The ‘loss’ of eleven days worried many people, and some were upset that festivals would no longer be held on the ‘right’date, i.e. precisely twelve months after they were last held (see Holy Thorn). An ‘Old Style’ date is eleven days later than the adjusted calendar; thus 10 October is an Old Style equivalent to Michaelmas (29 September), while 6 January is both the Feast of the Epiphany or Twelfth Night in its own right (New Style) and the Old Style equivalent of Christmas (25 December).

Quarter Days were four dates marking the beginning or end of legal contracts, especially between landlord and tenant or employer and employee. In England they were Lady Day (25 March), Midsummer Day (24 June), Michaelmas (29 September), and Christmas Day.

A sculptured or painted emblematic series of the months.

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calendars Virtually all peoples have used the lunar month as a measure of time, although, since this period comprises 29 ½ days, the months inaugurated by each new moon cannot contain a constant number of whole days. The succession of seasons is determined by the yearly cycle of the earth around the sun in roughly 365¼ days, that is, the solar year, which is about eleven days longer than twelve lunar months. Hence, when the solar year is divided into twelve months, the beginning of each month cannot in general correspond exactly with the appearance of the new moon.

The Greek calendar

All Greek states had a civil year of twelve months with 29 and 30 days alternately, each month beginning with the new moon. Since the year thus contained only 354 days, adjustment to fit the solar year had to be made, and the magistrates did this by adding (‘intercalating’) extra months or fractions of months as need arose.

The civil year at Athens began in July and was named after the chief archon. The days within the Greek month or the prytany were sometimes divided into three periods of (mostly) ten days (decades) and the days within each decade denoted by number, but there were many variations.

The Roman calendar

The original Roman calendar ran from March to December (‘month ten’, decem), with an uncounted gap in the winter when no agricultural work was possible. By Caesar's day the Roman year consisted of 355 days divided into twelve months, which corresponded with neither the sun nor the moon, and by 46 BC the civic and solar years were discrepant by about three months. Caesar gave the year 46 BC 445 days to remove the discrepancy, and from 1 January 45 made the year consist of 365 days, with the individual months having essentially the same length as in the modern calendar; he also introduced the leap year. In this Julian calendar the year is about eleven minutes longer than the solar year, and by the late sixteenth century the accumulated difference amounted to ten days; accordingly Pope Gregory XIII omitted ten days from 1582 and suggested that three intercalary days be omitted every four hundred years. The modern calendar is essentially the Julian, which is still used for dates before 1582.

The Romans dated their year by the names of the consuls. The method of dating by magistrates is only effective if the series of names continues uninterrupted. Dating by eras, where the years are numbered consecutively from an agreed starting-point, e.g. the foundation of Rome, has obvious advantages. In the fifth century BC some Greeks had used to establish an era the Olympian games, whose first recorded victor won in 776 BC and which recurred every four years. The numbering of Olympiads (the four-year periods between games) and the counting of years within an Olympiad probably goes back to the third century BC, and this system lasted until the Byzantine age. The Romans did not widely use the era ab urbe condita (‘from the foundation of Rome’, abbreviated to AUC), perhaps because the date we now accept as traditional, 753 BC, was disputed.

The method of dating by the years of the Christian era was introduced in the mid-sixth century by Dionysius Exiguus, a Scythian monk who lived at Rome.

During the Middle Ages there were in France, as elsewhere in Europe, different ways of fixing the beginning of the year, the main dates being 25 December, 1 January, 25 March, and Easter. An edict of Charles IX of 1 January 1563/4 prescribed 1 January as the standard date. A few years later, in 1582, the Gregorian calendar was adopted in place of the Julian, with the consequent loss of 10 days.

1792 saw the introduction of a quite new calendar to mark the inauguration of the Republic on 22 September (1 Vendémiaire, An I). At first, the Republican era was deemed to have begun on 1 January 1792, so that documents from 1 January 1793 to 21 September 1793 were dated An II, but it was decreed in October 1793 that An I had begun with the declaration of the Republic on 22 September 1792. The Revolutionary calendar came into general use in December 1793 and was abolished by Napoleon in 1805, France returning to the Gregorian calendar on 1 January 1806 (12 Nivôse, An XIV).

Under the Revolutionary calendar, the year was divided into twelve months of 30 days, each of them divided into 3 décades, in which the days bore arithmetical names (primidi, duodi). The extra five or six days a year were observed as festivals known as sans-culottides. The months were given poetic new seasonal names devised by Fabre d'Églantine: Vendémiaire, Brumaire, Frimaire, Nivôse, Pluviôse, Ventôse, Germinal, Floréal, Prairial, Messidor, Thermidor, Fructidor.

[Peter France]

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A formal system for measuring and documenting the passage of time. The basic unit of nearly all known calendars is the cyclical movement of the sun, giving the units known in the modern western world as days, and—rather less easy to gauge—the annual cycle or solar year. In ancient Egypt, for civil purposes, a solar calendar of 365 days to the year was used in which there were 12 months of 30 days and 5 intercalary days. For agricultural purposes, and for determining the timing of religious festivals, a second calendar was used, based on observations of the dog star Sirius (Sothis to the Egyptians). The annual heliacal rising (i.e. at the same time as the sun) usually preceded the Nile flood. The two calendars would coincide every 1460 years, a period known as the Sothic Cycle. The cycle of the moon provides a lunar month and this was used as the basis for the calendar in ancient Mesopotamia, where 12 months of 29.5 days were adjusted over 19 cycles to keep the calendar in step with solar years. How these basic units were divided, combined, and reconciled is culturally specific, and many different systems have been developed. All, however, fall into one of two main types.

Linear calendars start from a nominated moment and extend outwards from that time in an endless sequence of more or less equal sized repetitive units. The western Christian calendar takes as its origin a notional point considered to be the Incarnation of Christ and extends linearly forwards (years ad from ad 1) and backwards (years bc from 1 bc). The reckoning system was established by Julius Caesar who adapted the Egyptian solar calendar to Roman usage, inserting extra days in the shorter months to make 365 days over 12 months with the insertion of an additional day into February every four years. The naming of the years was first established in Italy in the 6th century ad and based on the Julian calendar; it was later revised by Pope Gregory XIII in ad 1582 to provide the calendar used today, which is known as the Gregorian calendar (adopted by Act of Parliament in Britain in ad 1752). Other linear calendars were established in classical times and more recently, and include: a Roman calendar with a notional start date fixed as the founding of Rome in years AUC (ab urbe condita) which can be mapped onto the Gregorian calendar as starting in 753 bc; a Greek calendar with a notional start date fixed as the first Olympiad which maps onto the Gregorian calendar as 776 bc; and an Islamic calendar based on the flight of Mohammad from Mecca to Medina (the Hegira). Hegira year 1 (AH 1) maps onto the Gregorian calendar as ad 622 but Hegira years are lunar years with a mean length of 354.3 days.

Cyclical calendars use a floating starting position which is periodically returned to. One of the most common is with reference to the reign of a king, queen, or other official so that dates are given as the regnal year of that person. When the person is replaced the calendar starts again for the next person. Ancient Chinese societies used a cyclical calendar of 60 years, designated by two ideographs in a series which covers the whole 60-year period before starting again. The Mayan calendar was based on a 52-year cycle (known as the calendar round) which combined a 260-day almanac and a 365-day year. The use of this system carried with it a belief that events, including disasters, repeated themselves with each turn of the cycle. See also time, long count.

The Celtic measurement of time appears to have assumed that darkness preceded light. Thus the Celtic calendar of pre-Christian times measured the year as beginning with the onset of winter. The Old Irish name for the first day of the new year is Samain, usually assumed to be 1 November in the Julian and Gregorian calendars (but 11 November in Gaelic Scotland). The beginning of the light half of the year was Beltaine, 1 May (or 15 May in Scotland). The dark half of the year was further divided by Imbolc, 1 or 2 February; and the light half of the year was divided by Lughnasa, 1 August (in Scotland sometimes as late as 29 September).

Key to our understanding of the Celtic measurement of time are the bronze tablets unearthed in 1897 at Coligny, 14 miles NNE of Bourg-en-Bresse (Ain) in eastern France, the most extensive document in the Gaulish language yet found (1st cent. AD) and now preserved at Lyons. They detail sixty-two consecutive months, approximately equal to five solar years. Months are thirty or twenty-nine days and are divided into halves. The lunar year of twelve months was adapted to the solar year by the intercalation of an extra month of thirty days every third year. Months are indicated either MAT [good or auspicious] or ANM [an abbreviation for anmat, not good]; remnants of this usage can be seen in the Welsh Triads which list certain events as mad [fortunate] or anfad [unfortunate].

Bibliography

• A. and B. Rees, “‘Light and Dark’”, ch. 3 of Celtic Heritage (London, 1961, 1973), 83–94
• Kevin Danaher, The Year in Ireland: Irish Calendar Customs (Dublin, 1977)
• Paul-Marie Duval, “‘Les Calendriers’”, in Recueil des inscriptions gauloises, iii (Paris, 1985)
• Garrett Olmsted, The Gaulish Calendar (Bonn, 1992)

In Russia, the calendar has been used not only to mark the passage of time, but also to reinforce ideological and theological positions. Until January 31, 1918, Russia used the Julian calendar, while Europe used the Gregorian calendar. As a result, Russian dates lagged behind those associated with contemporary events. In the nineteenth century, Russia was twelve days behind, or later than, the West; in the twentieth century it was thirteen days behind. Because of the difference in calendars, the Revolution of October 25, 1917, was commemorated on November 7. To minimize confusion, Russian writers would indicate their dating system by adding the abbreviation "O.S." (Old Style) or "N.S." (New Style) to their letters, documents, and diary entries.

The Julian Calendar has its origins with Julius Caesar and came into use in 45 B.C.E. The Julian Calendar, however, rounded the number of days in a year (365 days, 6 hours), an arithmetic convenience that eventually accumulated a significant discrepancy with astronomical readings (365 days, 5 hours, 48 minutes, 46 seconds). To remedy this difference, Pope Gregory XIII introduced a more accurate system, the Gregorian Calendar, in 1582.

During these years Russia had used the Byzantine calendar, which numbered the years from the creation of the world, not the birth of Christ, and began each new year on September 1. (According to this system, the year 7208 began on September 1, 1699.) As part of his Westernization plan, Peter the Great studied alternative systems. Although the Gregorian Calendar was becoming predominant in Catholic Europe at the time, Peter chose to retain the Julian system of counting days and months, not wanting Orthodox Russia to be tainted by the "Catholic" Gregorian system. But he introduced the numbering of years from the birth of Christ. Russia's new calendar started on January 1, 1700, not September 1. Opponents protested that Peter had changed "God's Time" by beginning another new century, for Russians had celebrated the year 7000 eight years earlier.

Russians also used calendars to select names for their children. The Russian Orthodox Church assigned each saint its own specific feast day, and calendars were routinely printed with that information, along with other appropriate names. During the imperial era, parents would often choose their child's name based on the saints designated for the birth date.

Russia continued to use the Julian calendar until 1918, when the Bolshevik government made the switch to the Gregorian system. The Russian Orthodox Church, however, continued to use the Julian system, making Russian Christmas fall on January 7. The Bolsheviks eliminated some confusion by making New Year's Day, January 1, a major secular holiday, complete with Christmas-like traditions such as decorated evergreen trees and a kindly Grandfather Frost who gives presents to children. Christmas was again celebrated in the post-communist era, in both December and January, but New Year's remained a popular holiday.

Bibliography

Hughes, Lindsey. (1998). Russia in the Age of Peter the Great. New Haven, CT: Yale University Press.

—ANN E. ROBERTSON

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It was widely recognized in the early sixteenth century that the calendar was inaccurate, but the question of how it should be reformed and who had the authority to do so raised fundamental issues. It was some two hundred and fifty years before all of Europe had changed.

The Christian Church had adopted the Julian calendar from the Roman Empire at the Council of Nicaea in 325 C.E.: the first general council of the church, its authority acknowledged thereafter by East and West, Protestants and Catholics. A slight error in the original Roman calculations had by 1500 accumulated to ten days, leaving the real spring equinox on 11 March instead of 21 March. What really bothered the Roman Catholic Church (though not, apparently, the Orthodox Church) was the error this produced in the date of Easter. This was supposed to fall on the Sunday on or after the full moon after 21 March, but it now often fell a month late relative to the real equinox. Nicolaus Copernicus's De Revolutionibus Orbium Caelestium (1543; On the revolutions of the celestial orbs) had originally been commissioned as a basis upon which to reform the calendar, but the intervening Reformation and Copernicus's heretical views about the solar system overlaid the issue.

One of the last acts of the Counter-Reformation Council of Trent was to order a reform of the calendar, which it was hoped would provide a basic measure of agreement between Protestants and Catholics on at least one fundamental issue. The observations and calculations were undertaken by the Jesuit astronomer Christoph Clavius (1537–1612), and the results embodied in Pope Gregory XIII's bull of 1582. Ten days were to be removed from October 1582 to bring the calendar back in line with the seasons, and the system of leap years was modified to keep it on track; from then on there was to be a leap year only at the end of every fourth century, and not of every century as before. The old formula for calculating the date of Easter was modified but retained. The Gregorian reform was fundamentally religious rather than astronomical, and the Roman Catholic Church continued to reject Copernicus.

Only a handful of countries (Spain, Portugal, Poland, and parts of Italy) adopted the new Gregorian calendar on time, not least because the bull was promulgated so late. By 1585 most Roman Catholic countries had followed. Most Protestant states—including large parts of Switzerland, Germany, the Protestant Low Countries, Great Britain, and Scandinavia—retained the Julian calendar for another century or more, creating a patchwork of calendrical practice throughout Europe, particularly complex in the Holy Roman Empire. The key issue was not astronomical accuracy but papal authority. By accepting a papal bull, states would appear to be recognizing the authority of the pope not only to interfere in civil affairs but also to alter decisions of the early church; indeed, most Roman Catholic countries took care to adopt the new calendar by their own civil acts. In England, the mathematician and astrologer John Dee (1527–1608) argued that the time of Christ, rather than that of the early church, was the appropriate "radix of time" for Protestants, and proposed his own Elizabethan imperial calendar one day ahead of Rome, but his views were unwelcome to the authorities and in the end England did nothing.

In 1700, with the gap between the two calendars set to widen to eleven days, most Protestant states followed a resolution of the imperial Diet of Regensburg and adopted a modified version of the Gregorian calendar. They did so using their own calculations, following the German astronomer Johannes Kepler (1571–1630), and substituting an astronomical Easter for the traditional version, to the same practical effect. In Britain, where antipopery remained strong, the new calendar was not adopted until September 1752, when eleven days were omitted and a third Easter calculation adopted, also to identical effect. Sweden pursued its own course, coming fully into line in 1753. The churches of the East remained unmoved, standing fast by the decisions of early Christendom; the fast-secularizing states of eastern Europe generally went Gregorian for civil purposes around the time of World War I.

Practical Problems

Did the calendar change create practical, as opposed to political, problems? Undoubtedly it did, especially in international communications and where Protestant and Catholic jurisdi