CalendarDB
108 entries on how humanity counts time: calendar systems from the Maya Long Count to the Hebrew and Islamic calendars, the eras years are numbered from, the reforms that skipped days, leap rules and cycles, months, weekdays and the festivals they set.
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Gregorian calendar
1582The Gregorian calendar is the civil calendar of nearly the whole world. Introduced by Pope Gregory XIII in 1582, it keeps the...
Julian calendar
1 January 45 BCEJulius Caesar's calendar, designed mainly by the astronomer Sosigenes of Alexandria, took effect on 1 January 45 BCE. It has...
Hebrew calendar
Calculated rules by...The Hebrew calendar has months of 29 or 30 days tied to the Moon and adds a thirteenth month, Adar I, in years 3, 6, 8, 11, 14...
Islamic Hijri calendar
c. 638 CE (17 AH)The Hijri calendar is purely lunar, with 12 months of 29 or 30 days and no intercalation, so it moves through the seasons in a...
Chinese calendar
104 BCE (Taichu)...The traditional Chinese calendar has months that begin at the new moon and inserts a leap month roughly every three years so that...
Maya Long Count
Earliest known date...The Long Count is a running tally of days in units of k'in (1 day), winal (20), tun (360), k'atun (7200) and b'ak'tun (144,000...
French Republican calendar
Decreed 24 October...Revolutionary France replaced the Gregorian calendar with twelve months of 30 days, each split into three ten-day décades, plus...
British calendar change of 1752
Calendar Act 1750...Under the Calendar (New Style) Act 1750, Great Britain and its colonies, including those in America, made Wednesday 2 September...
Swedish calendar, 1700–1712
1700Sweden planned to reach the Gregorian calendar gradually by omitting every leap day from 1700 to 1740. It dropped the 1700 leap...
Ethiopian calendar
Ethiopia's official calendar has twelve months of 30 days plus Pagume, a thirteenth month of five or six days. Its leap year...
Easter
Computus fixed after...Easter falls on the first Sunday after the ecclesiastical full moon on or after 21 March. In the Gregorian calendar Western...
Unix time
Epoch 1970-01-01...Unix time counts seconds since 00:00:00 UTC on 1 January 1970, ignoring leap seconds. It underlies timestamps in most computer...
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From the Blog
In September 1752 Britain and its colonies jumped from the 2nd to the 14th. Here is why it took 170 years, and what the change left behind.
How Leap Year Rules Work Across CalendarsFrom the Julian four-year rule to the Hebrew 19-year cycle and the Islamic 30-year cycle, every calendar needs a way to absorb leftover time.
The 344-Year Road to a Global CalendarCatholic Europe switched in 1582, Turkey adopted Gregorian years in 1926. A tour of who adopted the Gregorian calendar when, and who still uses another.