99 Fun Facts About Calendar

What did the Romans call the first day of every month?

Kalends: debts fell due on that day, and the account book that tracked them, the calendarium, gave English the word calendar.

Which Roman leader stretched one year to 445 days to fix the calendar?

Julius Caesar added the extra days in 46 BC because Rome's calendar had slipped about three months out of step with the seasons; his new calendar took over the next year, built to stay in step without further tinkering.

Which pope issued the 1582 bull Inter gravissimas that reformed the calendar?

The bull was dated 24 February 1582 and the new calendar took effect that October.

Which country skipped straight from 4 to 15 October 1582, adopting the pope's new calendar at once?

Spain made the jump on the first possible night. Teresa of Ávila died there that night, between 4 and 15 October, and 15 October is now her feast day.

Which English writer died on 23 April 1616, a day that Catholic Europe was already calling 3 May?

William Shakespeare died under England's old calendar, then ten days behind; Cervantes, long given the same death date, in fact died more than a week before him.

Leap years exist because Earth's orbit takes 365 days plus roughly how much extra time?

6 hours is the rounded figure: the true excess is about 11 minutes less, an error the old calendar ignored until it had piled up to ten days by 1582.

Century years such as 1900 skip their leap day unless they divide evenly by which number?

400 is the test, so 1700, 1800 and 1900 had no leap day but 2000 did; anyone born on a leap day in 1896 had to wait until 1904 for a true birthday.

When the American colonies switched calendars in 1752, which future president's birthday moved from 11 to 22 February?

George Washington was born on 11 February 1731 by the old reckoning; the switch dropped eleven days and moved the start of the year, so his birth date became 22 February 1732.

Which country's tax year begins on 6 April, a leftover from its switch of calendars in the 18th century?

Britain's tax year once turned on Lady Day; when eleven days were dropped in 1752 the Treasury kept its year at full length by moving its dates on by eleven days, into April.

Which satirist's painting An Election Entertainment underpins the 'Give us our eleven days!' riot myth?

William Hogarth painted a stolen Tory banner reading 'Give us our Eleven Days' into a 1755 tavern scene; no record of any actual calendar riot has ever been found.

When Soviet Russia switched to the Gregorian calendar in February 1918, how many days were dropped?

Wednesday 31 January was followed by Thursday 14 February, and Julian dates had to be written in brackets until July.

Which country's calendar contained a 30 February in 1712?

Sweden dropped its 1700 leap day to begin a gradual switch, kept the next two in error, then gave up and added a second leap day in 1712 to return to the old calendar.

Which US state switched calendars and sides of the International Date Line when it changed owner?

Alaska passed from Russia to the US on 18 October 1867, trading the Julian calendar for the Gregorian and the Asian side of the date line for the American; the date is still kept as Alaska Day.

The legendary calendar of Romulus had ten months and began in spring with which month?

March opened Romulus's ten-month year, which ran only to December; the winter days that followed belonged to no month at all.

Which Roman king is traditionally credited with adding the months of January and February?

The addition, around 713 BC, brought the calendar up to a 354-day lunar year.

Which month is named after the Roman god of doorways and gates?

January honours Janus, god of doorways and beginnings; from 153 BC Rome's consuls took office on its first day, fixing it as the start of the official year.

The Roman month Quintilis was renamed in 44 BC and is known today by which name?

July honours Julius Caesar, who was born in the month then called Quintilis; it was renamed for him in 44 BC, the year he was assassinated.

Which month did the Roman Senate rename in 8 BC in honour of Rome's first emperor?

August was called Sextilis until the Senate renamed it for Augustus, choosing the month of his greatest triumphs, among them the conquest of Egypt.

September's name comes from the Latin word for which number?

Seven is septem in Latin: September was the seventh month of the early Roman year and kept the name even after the year's starting point moved and made it the ninth.

Which day of the week is named after Tiw, the one-handed Germanic god the Romans equated with Mars?

Tuesday is 'Tiw's day'. In Norse myth, where he is called Týr, he lost the hand to the wolf Fenrir, having put it in the beast's jaws as a pledge while the gods bound it.

Wednesday takes its name from which Germanic god?

Woden is the Old English name for Odin; 'Woden's day' was coined to translate the Roman day of Mercury, which is why French calls it mercredi.

Under the ISO 8601 standard, which day is treated as the first day of the week?

Monday is day 1 under ISO 8601, so the standard's weekend really does end the week; the older Jewish and Christian count makes it the second day instead.

In the ISO week-date system, week 1 of a year is defined as the week containing the year's first what?

Equivalently, it is always the week that contains 4 January.

How many years in every 400-year cycle have a 53rd ISO week?

They are the years containing 53 Thursdays; the ISO year can start as early as 29 December.

The traditional Chinese calendar is which type of calendar?

Lunisolar: months follow the lunar phases, and a 13th month is slipped into some years so that the New Year always falls in late winter instead of drifting through the seasons.

According to legend, which animal won the Jade Emperor's race and got the first year of the zodiac cycle?

The Rat won, in the best-known telling, by hitching a ride across the river on the Ox's back and jumping off at the last second, which is why the Ox comes second.

The Hebrew calendar numbers its years from which event?

The Creation is the count's starting point, a date rabbis worked out from the Bible; before it took hold, Jewish scribes dated their contracts by the Greek era of the Seleucid kings.

The Islamic calendar is tied to the cycles of which heavenly body alone?

The Moon alone sets the Islamic year of 354 or 355 days, some 11 days short of the solar year, so Ramadan passes through every season in about 33 years.

The Islamic calendar counts its years from Muhammad's migration from Mecca to which city?

Medina took Muhammad in during 622, but he never used the count himself: it was introduced some 17 years later and backdated to the year of his arrival.

Which country's official calendar begins each year on the first day of spring, the festival of Nowruz?

Iran's Nowruz, 'new day' in Persian, has Zoroastrian roots; Iranians see out the old year by leaping over bonfires in its final week.

Which civilisation's Long Count calendar completed a great cycle on 21 December 2012, sparking doomsday claims?

The Maya left only two known inscriptions that mention the date, and neither predicts an ending: for them the Long Count simply rolled over into a new cycle.

Which inscription is one of only two known Maya references to the 13th bʼakʼtun ending in 2012?

The other is a stairway block at La Corona; scholars call the doomsday reading 'a complete fabrication'.

The French Republican calendar divided each 30-day month into three ten-day cycles called what?

Décades replaced the seven-day week, so the day of rest came only every tenth day instead of once a week, until the old week was restored in 1802.

Which month of the French Republican calendar gave its name to the 1794 coup that toppled Robespierre?

Thermidor, from the Greek for heat, was the calendar's high-summer month; on its ninth day in 1794 the Convention shouted Robespierre down and ordered his arrest, ending the Terror.

The French Republican calendar gave every day a plant, animal or tool in place of what?

A saint: to loosen the Church's hold, the poet Fabre d'Églantine swapped each saint's day for a farm name, giving every fifth day an animal and every tenth a tool.

Which African country's calendar has twelve 30-day months plus a short thirteenth, and runs seven or eight years behind?

Ethiopia dates the birth of Jesus seven or eight years later than the Western count, so it rang in its year 2000 with street parties in September 2007.

Astronomers' Julian day numbers count from noon on 1 January of which year?

Joseph Scaliger picked it as the last time three ancient cycles all began together, safely before any historical record.

The Modified Julian Date, introduced in 1957 to log Sputnik's orbit, equals the Julian Date minus what?

It shifts the epoch to midnight on 17 November 1858, small enough to fit in 18 bits on an IBM 704.

In the BC/AD system, which year comes immediately after 1 BC?

AD 1 follows 1 BC directly because the count has no year zero; astronomers put one back for their sums, calling 1 BC 'year 0' and 2 BC 'year -1'.

Which spreadsheet program treats 1900 as a leap year, a bug kept for Lotus 1-2-3 compatibility?

Microsoft Excel copied the Lotus error on purpose so old files would open with the same dates; correcting it now would move almost every date in existing workbooks back a day.

Which country deleted 30 December 2011 from its calendar to move west of the International Date Line?

Samoa jumped west to share a working week with Australia and New Zealand, undoing a move the other way in 1892 that had lined it up with traders from the United States.

Which mathematician devised the Doomsday rule for finding any date's weekday?

John Conway adapted the rule from a Lewis Carroll method; he had his computer quiz him with random dates at every login and could usually name the weekday in under two seconds.

Which holiday always falls on the year's Doomsday, the same weekday as 4/4, 6/6, 8/8, 10/10 and 12/12?

Halloween is exactly three weeks after 10/10, so it shares that weekday; US Independence Day and Boxing Day sit on the same day too, so all three match every year.

Who created the World Calendar, with its equal 91-day quarters, in 1930?

Its extra day, 'Worldsday', sits outside the week; the campaign reached the US Congress and the United Nations.

Which camera company ran its business on a 13-month calendar from 1928 until 1989?

Kodak's founder George Eastman championed a plan for 13 identical 28-day months, and his firm kept using it for half a century after the League of Nations dropped the idea in 1937.

Despite its name, which twice-yearly event has a day slightly longer than its night?

The equinox means 'equal night', but the sun's width and the bending of its light by the air stretch the day; truly equal day and night, the 'equilux', comes a few days before the spring one.

At the June solstice the sun is overhead at about 23.4° north, a line known as what?

The Tropic of Cancer was named when the June solstice sun stood in the constellation Cancer; the slow wobble of Earth's axis has since carried the sun out of it.

Which Texas town declared itself the 'leap year capital of the world' in 1988?

It also launched an international birthday club for 'leaplings' born on 29 February.

In which Gilbert and Sullivan opera is Frederic, born on 29 February, bound to serve until his 21st birthday?

The Pirates of Penzance turns on the catch: Frederic has lived 21 years but had only five birthdays, so his apprenticeship has more than half a century left to run.

A calendar month contains a Friday the 13th only when it begins on which weekday?

Sunday is the giveaway: any month that opens on one must put its 13th on a Friday. Every year has at least one such month and never more than three.

In dates such as AD 1066, what does the abbreviation AD, devised by a sixth-century monk, stand for?

Anno Domini is Latin for 'in the year of the Lord'. The popular guess 'After Death' cannot work, since it would leave the years of Jesus's own life in neither BC nor AD.

Irish legend says Saint Brigid persuaded which fellow saint to let women propose on leap day?

Patrick is said to have offered far less at first, until Brigid haggled him down to one day every four years. The custom itself is not recorded before the 19th century.

Which Spanish novelist is traditionally given Shakespeare's death date, 23 April 1616, yet died on a different day?

Miguel de Cervantes was buried on 23 April in Gregorian Spain, while Shakespeare's 23 April was a Julian date some days later. UNESCO chose the shared date for World Book Day.

Russia's October Revolution of 1917 took place in which month by the Gregorian calendar used today?

November is when the uprising happened by the modern count. Russia still ran on the older Julian calendar, which had slipped behind, so the name kept the month Russians saw on the wall.

Police in which US city popularised the name Black Friday for the traffic chaos after Thanksgiving?

Philadelphia officers used the name for the crowds and jams that opened the Christmas shopping season. In 1961 the city's merchants tried rebranding the day 'Big Friday', which nobody adopted.

Which Jules Verne hero wins a £20,000 wager because travelling east around the globe had gained him a day?

Phileas Fogg believes he is five minutes late, but heading east meant he saw 80 sunrises while London saw only 79, so he still reaches the Reform Club in time.

Which Christian festival's date depends each year on the first full moon on or after the spring equinox?

Easter moves because a church formula hunts for that full moon, so the feast can land anywhere across five weeks. Keeping it tied to the equinox was the reason for the calendar reform of 1582.

Which tyre maker has issued a limited-edition photography calendar, trademarked as The Cal, since 1964?

Pirelli never puts it on sale: the 20,000 or so copies printed each year go out as gifts to celebrities and chosen customers. The idea came from its British subsidiary, not Milan.

A second full moon falling within a single calendar month is popularly known by which colour?

Blue moon gained this meaning by mistake: a 1946 magazine article misread an older, fiddlier rule, and the simpler version stuck. An extra full moon turns up every two or three years.

Which ninth month of the Islamic year drifts through every season because the calendar is purely lunar?

Ramadan slides through the seasons over about 33 years, so a Muslim keeps its dawn-to-dusk fast on the long days of midsummer and, some years later, the short days of midwinter.

Which Jewish festival opens the Hebrew civil year in autumn with blasts on the shofar, a ram's horn?

Rosh Hashanah starts the year in the seventh month, not the first: the Hebrew calendar counts its months from spring but changes its year number in autumn.

Which festival, kept at the spring equinox for over 3,000 years, takes its name from the Persian for 'new day'?

Nowruz has Zoroastrian roots and opens the year on Iran's calendar, with celebrations stretching from the Balkans to Central Asia.

Which Chinese celebration, held under the first full moon of the year, closes the New Year festivities?

Lantern Festival falls on the fifteenth day of the first month, when streets glow with lanterns and families eat tangyuan, sticky rice balls with sweet fillings.

Advent calendars, counting down to Christmas, were first used in the 1800s by Lutherans in which country?

Germany's Lutherans began the custom, and the familiar card version with 24 little doors hiding pictures followed in the twentieth century.

Which prehistoric English stone circle is aligned to the midsummer sunrise and the midwinter sunset?

Stonehenge may have mattered most in midwinter: animal bones from feasts held nearby suggest people gathered there around the shortest day rather than the longest.

At which Maya city does the pyramid El Castillo cast a serpent-shaped shadow around each equinox?

Chichen Itza draws thousands to watch the shadow snake slide down the staircase. The pyramid is often read as a calendar in stone: four stairways of about 91 steps plus the top platform make 365.

A 2,000-year-old geared 'computer' for tracking the Sun and Moon was raised in 1901 off which Greek island?

Antikythera gave its name to the mechanism, found in a shipwreck and now ranked the oldest known analogue computer: its bronze gears predicted eclipses and tracked the four-year cycle of athletic games.

Which Scots word names the last day of the year, when 'first-footing' begins straight after midnight?

Hogmanay luck rides on the first-foot, the first guest over the threshold: tradition prefers a tall, dark-haired man, and some east coast fishing towns once had him carry a decorated herring.

One theory says which annual custom began as mockery of people who kept France's old spring New Year?

April Fools' Day, on this telling, mocked those still feasting at the start of April after France fixed New Year on 1 January in 1564. Historians rank it as one theory among several.

Which monk, working in Rome in 525, first numbered the years from the birth of Jesus?

Dionysius Exiguus wanted to stop dating years by Diocletian, an emperor who had persecuted Christians. His count sat in church tables for centuries before it came into wide use.

Ancient Egypt's year was probably pegged to the dawn return of which star, herald of the Nile flood?

Sirius came back into the dawn sky just as the Nile began to rise. With no leap years, Egypt's 365-day civil calendar then slipped against the star, taking about 1,460 years to come full circle.

North Korea's Juche calendar, in use from 1997 to 2024, counted its years from the birth of which leader?

Kim Il Sung was born in 1912, which became Juche 1. The decree came on the third anniversary of his death, and the state reportedly went back to plain Gregorian years in 2024.

Which island's official calendar numbers its years from 1912, the founding year of the Republic of China?

Taiwan dates official documents in Minguo years, which made 2011 its year 100. Sun Yat-sen set the count running when the republic was founded on the mainland.

Japan counts years by imperial era; which era began on 1 May 2019 when Naruhito took the throne?

Reiwa takes its characters from the Man'yoshu, an eighth-century poetry anthology, and it split 2019 in two: the year opened as Heisei 31 and ended as Reiwa 1.

Which South Asian country's civil calendar, the Vikram Samvat, runs about 57 years ahead of the Gregorian?

Nepal uses a solar version for everyday dates, so most of 2025 was its year 2082. In India the same era survives mainly for fixing religious festivals.

Which religion's calendar divides the year into nineteen months of nineteen days, plus a few spare days?

Baháʼí Faith months are named for attributes of God, and the four or five leftover days slot in before the final month to round out the solar year.

Which major Romance language numbers its weekdays, 'second' to 'sixth', rather than naming them after planets?

Portuguese counts from segunda-feira to sexta-feira and keeps proper names only for the weekend, sábado and domingo.

The word calendar comes from the Roman kalends, the debt-paying day that fell on which day of each month?

First day it was: on the kalends, priests announced how long the new month would run and debtors had to settle up, in account books called kalendaria.

What is the name for the point in early January when Earth swings closest to the Sun?

Perihelion comes about two weeks after the December solstice, in the depth of northern winter: the seasons follow Earth's tilt, not its distance, though sunlight is then about 7% stronger.

Groundhog Day, held every 2 February, grew out of weather lore tied to which Christian feast that day?

Candlemas sunshine meant a longer winter in central European folklore, where the forecasting animal was a badger. Settlers in Pennsylvania handed the job to the local groundhog.

Until 1752 England's legal year began on the Annunciation feast, a quarter day traditionally called what?

Lady Day is why the UK tax year ends on 5 April: when the calendar jumped forward in 1752, the old year-end was shifted by the missing days so that nobody lost out.

Which yearly US publication, printed since 1792, has a hole punched in its corner for hanging on a nail?

Old Farmer's Almanac founder Robert B. Thomas began drilling the hole himself. His secret weather-forecasting formula is kept in a black tin box at the offices in Dublin, New Hampshire.

The 'Year 2038 problem' affects computers that count seconds from the start of 1970, a clock named after which system?

Unix time will overflow its signed 32-bit counter at 03:14:07 UTC on 19 January 2038, and unpatched systems will read the next second as a date in December 1901.

Ancient Greek historians dated events by which four-year unit, counted from games first held in 776 BC?

Olympiad counting gave Greek historians dates that did not depend on each city-state's own calendar. One writer even placed the founding of Rome in the first year of the seventh.

Which Pacific nation moved the International Date Line east in 1995 so all its islands shared one day?

Kiribati's move made its Line Islands the first land to greet each new year, and remote Caroline Island was renamed Millennium Island in time for 2000.

Which term names the anniversary that Canada, founded by Confederation in 1867, celebrated in 2017?

Sesquicentennial celebrations, branded Canada 150, cost the federal government an estimated half a billion dollars in events and building projects.

What term describes slipping an extra day or month into a calendar to keep it in step with the seasons?

Intercalation ranges from the single leap day added to February to the whole extra month that the Hebrew calendar slips in every second or third year.

Which crusading order's mass arrest on Friday 13 October 1307 is often cited as the root of an unlucky date?

Knights Templar were seized at dawn on the orders of France's Philip IV, a king deep in debt to them. No record pairs the day and the number as unlucky before the 19th century, so the link is doubtful.

Which US president moved Thanksgiving a week earlier in 1939 to give shops a longer Christmas season?

Franklin Roosevelt's change was derided as 'Franksgiving', and for three years the states split, some carving the turkey a week before the rest, until Congress fixed the date in 1941.

The full moon nearest the autumn equinox takes its traditional name from which farm task?

Harvest moon evenings have almost no dark gap between sunset and moonrise for several days running, which once let field hands keep working to bring the crops in.

Which zodiac sign opens the astrological year, with the Sun entering it at the northern spring equinox?

Aries, the ram, covers the first 30 degrees of the zodiac, and the same stretch of the Sun's path is the first month of Iran's solar calendar.

Which religious group's 'plain calendar' numbers the days and months to avoid names taken from pagan gods?

Quakers took up the habit in 1650s England and kept it well into the twentieth century, so a meeting might be set for Fourth Day of Tenth Month.

Which Persian poet-astronomer sat on the committee whose Jalali calendar a Seljuk sultan adopted in 1079?

Omar Khayyam ran the sultan's observatory at Isfahan and measured the solar year so precisely that his work became the basis of Iran's modern calendar.

Which 19-year cycle, named after an Athenian astronomer, returns the Moon's phases to the same dates?

Metonic arithmetic, 235 lunar months to almost exactly 19 solar years, drives the Hebrew calendar, which schedules its thirteen-month years on that pattern.

Napoleon's 1799 seizure of power is known by its French Republican calendar date, the 18th of which month?

Brumaire, the 'misty' month of late autumn, named the bloodless coup that toppled the Directory and made Napoleon First Consul. Karl Marx later borrowed the date for the title of a famous essay.

Fortnight preserves the old habit of counting by nights; which archaic English word did the same for one week?

Sennight squeezes a week's worth of nights into one word, a relic of the Anglo-Saxon custom of reckoning time by nights rather than days.

The International Fixed Calendar's thirteenth month, slotted between June and July, was given which name?

Sol was chosen in homage to the sun, since the new month took in midsummer. Every month then ran exactly four weeks, so each date fell on the same weekday year after year.

Which French philosopher's 1849 calendar had thirteen months named after great figures such as Moses and Homer?

Auguste Comte, the founder of positivism, also named every single day after a notable person and kept the year's last day outside the weekly cycle as a festival for the dead.

Which country marks its traditional new year, Songkran, with three days of public water fights in closed-off streets?

Thailand treated Songkran as the official start of the year until 1888, and only moved New Year's Day to 1 January in 1940. The soaking stands for ritual cleansing.