#e <t>calendar<d>4004 Oct 23<n>Ussher's creation date<c>Mesopotamia<info>This is the date when Bishop James Ussher (in A.D. 1611) reckoned time began.
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#p <nat>French<o>scholar<n>Joseph Justus Scaliger<b>1540<d>1609<info>Scaliger was a Calvinist scholar and a bitter opponent of the Gregorian calendar reform.
#bc
#e <t>calendar<d>4713 Jan 1<n>start of Scaliger's Julian cycle<info>The proleptic Julian date January 1, 4713 B.C. is the start of Scaliger's Julian cycle, now used extensively by astronomers. (The Twistory application also uses them internally.)
#e <t>calendar<d>3114 Aug 13<n>start of great Mayan cycle<c>Central America<info>August 13, 3114 B.C. is the first day of the Mayan long-count calendar. It consists of 13 "baktuns" of 144,000 days each.
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#e <t>calendar<d>2012 Dec 23<n>end of great Mayan cycle<c>Central America<info>The long-count calendar of the Mayan civilisation consists of 13 "baktuns" of 144,000 days each. The cycle began in about 3114 B.C.
#bc
#e <t>calendar<d>2100<n>360-day calendar<c>Sumer<info>Sumerians use a 360-day calendar.
#e <t>calendar<d>432<n>Metonic cycle<c>Athens<info>The greek astronomer Meton discerned a 19-year period over which lunar phases repeat on nearly the same calendar dates.
#e <t>calendar<d>238<n>365.25-day year proposed<c>Alexandria<info>Ptolemy III ordered a 365.25-day calendar, but the quarter day is not accepted by the priest caste.
// Rome
#e <t>calendar<d>735<n>1 A.U.C.<c>Rome<info>735 B.C. corresponds to 1 A.U.C., or "ab urbe condita," which is Latin for "from the founding of the city." Romulus initiated a 304-day calendar of 10 months.
#e <t>calendar<d>700<n>January and February added<c>Rome<info>King Numa, Romulus' successor, adds Januaris and Februaris to the calendar, bringing it to 355 days. (Months had 29 or 30 days each, to correspond to the length of a lunar month.)
// Julian calendar
#e <t>calendar<d>46 May(2)<n>Julian reform<au>Julius Caesar<c>Rome<info>Julius Caesar orders a reform of the calendar, based on a proposal by the Alexandrian astronomer Sosigenes. He institutes a 365.25-day year, with a leap year every four years.
#e <t>calendar<d>46 Jan<e>46 Dec<n>"Year of Confusion"<au>Julius Caesar<c>Rome<info>Julius Caesar began a reform of the calendar in 46 B.C., the so-called "Year of Confusion." The new year was moved from its traditional date in March to January 1. The traditional solstice had been March 25, but the calendar had drifted off in previous years. So two months were added in between November and December 46 B.C. to return it to its proper date starting in 45 B.C. In all, 46 B.C. was 445 days long.
#e <t>calendar<d>44<e>8<n>Leap years every three years<c>Rome<info>The Roman college of pontiffs strayed from Julius Caesar's decree, and began putting a leap year every three years instead of every four.
#e <t>calendar<d>8<e>A.D. 8<n>No leap years<c>Rome<info>Three leap years were skipped in order to correct the Julian calendar.
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#e <t>coin<d>8<n>"August"<c>Rome<info>The Roman senate renames the eighth month, Sextilius, to August, in honour of Caesar Augustus. (Sextilius had been the sixth month before the new year was moved to January in 46 B.C.) They added a day to August to give it 31 like July, which honours Julius Caesar. The extra day was taken from February.
#e <t>calendar<d>321<n>Romans adopt 7-day week<c>Rome<info>Constantine adopts the 7-day week for the Roman world, with Sunday as the worship day. Previously, the Romans had used an 8-day cycle to govern market days.
#e <t>calendar<d>531<n>A.D. dating system<au>Exiguus<info>Dionysius Exiguus introduces the "anno domini" (A.D.) dating system in a letter to bishop Petronius. Previously, the "anno Diocletiani," counting from the reign of emperor Diocletian, was commonly used. Dionysius wrote that he "preferred to count and denote the years from the incarnation of our Lord, in order to make the foundation of our hope better known and the cause of the redemption of man more conspicuous." Dionysius calculated that Christ had been born 531 years before, but how he arrived at this figure is unknown. It is generally accepted now that Christ was born between 6 and 4 B.C., according to this system.
// Gregorian calendar
#p <nat>Italian<o>physician<n>Aloysius Lilius<b>1510(2)<d>1575(1)<info>Lilius devised the reformed calendar which became know as the Gregorian calendar. According to the Alfonsine tables, which were reasonably accurate, the Julian calendar had one day too many about every 134 years. Desiring a rule which is easy to remember, he designed a reform to the Julain calendar which would skip three leap years every 400 years. After he died, his brother Antonio presented his plan to the papal calendar commission.
#e <t>calendar<d>1344 Sep 25<n>calendar reform ordered<c>Vatican<info>Pope Clement VI orders scholars to devise a plan to reform the calendar.
#e <t>calendar<d>1345<n>calendar reform proposal<info>Jean de Meurs and another scholar named Firmin reply to pope Clement's letter. They recommend that to correct the solar calendar, a number of days be removed all in one year. But they caution that it could be a controversial issue. The 19-year lunar calendar was in error too, since it had an error of an extra day approximately every 310 years. They recommended correcting the lunar calendar by removing four days in 1349, the first year of the next Metonic cycle. It appears that this reform was going to be implemented, until the Bubonic plague swept through Europe in 1347.
#e <t>decree<d>1582 Feb 24<n>Papal bull concerning calendar reform<aka>"Inter gravissimas"<c>Vatican<info>This decree mandated the Gregorian calendar reform later that year. The bull is called "Inter gravissimas" after its first line in Latin.
#e <t>calendar<n>Gregorian calendar reform<c>Vatican<d>1582 Oct 15<info>October 15, 1582, was the first date of the Gregorian calendar. The preceeding day was October 4 in Julian calendar.
#e <t>Gregorian reform<d>1582 Oct 15<c>Italy<n>Italy
#e <t>Gregorian reform<d>1582 Oct 15<c>Spain<n>Spain
#e <t>Gregorian reform<d>1582 Oct 15<c>Portugal<n>Portugal
#e <t>Gregorian reform<d>1752 Sep 14<c>London<n>Britain<info>Britain and her colonies adopt the Gregorian calendar by order of parliament. The new year is also moved from March 25 to January 1, which by then all other European countries were using.
#e <t>Gregorian reform<d>1915<c>Baltic States<n>Baltic States<info>Latvia, Lithuania and Estonia adopt the Gregorian calendar.
#e <t>Gregorian reform<d>1918 Feb 14<c>Russia<n>Russia
#e <t>Gregorian reform<d>1924<c>Greece<n>Greece
#e <t>Gregorian reform<d>1873<c>Japan<n>Japan
#e <t>Gregorian reform<d>1949 Oct 1<c>Beijing<n>China<au>Zedong<info>Mao Zedong imposes Gregorian calendar on China.
#e <t>calendar<d>1582 Nov<n>Orthodox synod<c>Constantinople<info>The Eastern Orthodox church rejects the Gregorian calendar reform.
#e <t>calendar<d>1923<n>Orthodox synod<c>Constantinople<info>The Eastern Orthodox church again rejects the Gregorian calendar reform, although some churches have begun using it around this time.
// Sweden
#e <t>calendar<d>1700 Feb<n>Sweden removes a leap day<c>Sweden<info>Sweden removes a leap day from the Julian calendar, as is called for in the Gregorian reform. They are now one day ahead of the Julian calendar, but still ten days behind the Gregorian.
#e <t>calendar<d>1712 Feb<n>Sweden adds February 30<c>Sweden<info>Sweden adds a February 30 to their calendar in 1712, thereby falling back in sync with the Julian calendar.
#e <t>Gregorian reform<d>1753<c>Sweden<n>Sweden
// Anno Hegirae
#e <t>calendar<d>622<n>A.H. era begins<c>Arabia<info>The anno hegirae (A.H.) era starts in A.D. 622. It is a purely lunar calendar of 354 days, or 355 in a leap year.
// French Revolutionary calendar
#e <t>calendar<d>1792<n>Revolutionary Year One<c>Paris<info>This is the first year of the French revolutionary calendar.
#e <t>decree<n>revolutionary calendar revoked by Napolean<c>France<d>1806
