100 Fun Facts About Calendar

Which Roman leader proposed the calendar reform of 46 BC that replaced the earlier Roman calendar?

The reform took effect on 1 January 45 BC and gave the year 365.25 days on average.

Which Alexandrian astronomer is considered the principal designer of the Julian calendar?

Pliny credits him; he may also have written the astronomical almanac Caesar published to help people use the new calendar.

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.

How many days were skipped in October 1582 when the reformed calendar took effect?

Thursday 4 October 1582 was followed directly by Friday 15 October, and the weekday cycle was left unbroken.

Which Calabrian doctor's proposal, after modification, became the basis of the 1582 calendar reform?

He died in 1576, so his brother Antonio presented the plan in Rome; the 'Lilian date' in computing counts days from 15 October 1582 in his honour.

What is the average length of a year in the Gregorian calendar?

That is 365 days, 5 hours, 49 minutes and 12 seconds; the calendar gains only about 0.1 day on the sun every 400 years.

Under the Gregorian rules, which of these years was NOT a leap year?

Centurial years are leap years only if divisible by 400, so 1700, 1800 and 1900 all skipped 29 February.

In September 1752, Wednesday the 2nd in Britain and its colonies was followed directly by which day?

Eleven days vanished; rents and wages were prorated so nobody gained or lost by the change.

Britain's 1750 calendar act is also known by the name of which lord who introduced it?

It was a private member's bill; the prime minister opposed it because he 'did not love new-fangled things'.

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

The only other source is a satirical journal run by the very lord who introduced the bill.

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?

It had skipped a leap day in 1700 planning a gradual switch, then gave up and gave 1712 two leap days to get back onto the Julian calendar.

When the US took over Alaska in October 1867, Saturday the 7th (Julian) became which Gregorian date?

The territory crossed the date line at the same time as it changed calendars, so the weekday went backwards; the anniversary is now Alaska Day.

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

Winter was simply left as an unassigned stretch of days before the next year began.

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.

January is named after which Roman god?

He is the god of beginnings and transitions, and the Saxons instead called the month Wulf-monath, 'wolf month'.

Before it was renamed in 44 BC to honour a Roman statesman born in it, July was known by which name?

The name meant 'fifth', since the year once began in March.

Which 13th-century scholar invented the tale that Augustus stole a day from February?

Sextilis already had 31 days before it was renamed in 8 BC.

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

It was the seventh month of the old Roman year, which is also why October, November and December are off by two.

Which day of the week is named after Tiw, a one-handed Germanic god of single combat and pledges?

He is the Norse Týr, and his day maps onto the Roman day of Mars.

Wednesday takes its name from which Germanic god?

He is Óðinn to the North Germanic peoples; the day corresponds to the Roman day of Mercury.

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

Many countries still count it as the second day, following the older Sunday-first tradition.

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?

Months start on the new moon, and a year has 12 or 13 of them so it stays roughly in step with the sun.

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

The Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog and Pig follow.

In Hebrew leap years, the 12th and 13th months are both known by what name?

Leap months come seven times in every 19-year Metonic cycle, and sources disagree on which of the two is the 'real' one.

How many days are in a year of the Islamic (Hijri) lunar calendar?

Because it is about 11 days short of the solar year, Ramadan drifts through all four seasons over roughly 33 years.

The Islamic era's epoch is the year Muhammad migrated from Mecca to Medina; in which year CE was that?

The migration is the Hijrah, and years are written AH, from the Latin Anno Hegirae.

Which caliph introduced a numbered Muslim era around 638 CE after an official complained letters had no year?

The complaint came from Abu Musa al-Ash'ari in Basra, who could not tell which instructions were most recent.

The Maya Long Count starts from a creation date equivalent to 11 August of which proleptic Gregorian year?

The system needed a zero placeholder, one of the earliest uses of the concept anywhere.

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?

Five or six complementary days, the Sansculottides, filled out the year after the twelfth month.

The Republican month Thermidor took its name from the Greek word for what?

It ran from mid-July to mid-August; the overthrow of Robespierre on 9 Thermidor gave the word its political meaning.

Who named every day of the French Republican year after plants, animals, minerals and tools?

The winter month Nivôse got minerals; the point was to crowd out the saints' days.

The Ethiopian calendar has twelve 30-day months plus a short thirteenth month, Pagume, of how many days?

The extra day comes every four years without exception, like the Julian calendar, so the year begins on 11 or 12 September.

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?

Astronomers avoid the gap by calling 1 BC 'year 0' and 2 BC 'year -1'.

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

Its date system even has an epoch of '0 January 1900', so the bug is preserved for backward compatibility.

On which date was the 27th leap second added to Coordinated Universal Time?

It was the 27th since 1972, putting UTC 37 seconds behind atomic time; a 2022 resolution called for ending leap seconds by 2035.

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

It wanted to share a business week with Australia and New Zealand, its biggest trading partners.

Which mathematician devised the Doomsday rule for the day of the week in 1973?

He drew on Lewis Carroll's perpetual calendar method and could answer 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?

US Independence Day and Boxing Day do too, and Valentine's Day in common years.

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 company ran its business on the 13-month International Fixed Calendar from 1928 until 1989?

George Eastman championed the plan; every month had exactly 28 days and started on a Sunday.

What is the term, coined around the 1980s, for the date when day and night really are the same length?

It differs from the equinox because of refraction and the sun's angular size, and a true one is rare.

At the June solstice the sun is overhead at about 23.44° north, a line known as what?

Six months later the subsolar point reaches 23.44° south instead.

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 The Pirates of Penzance, leap-day-born Frederic's 21st birthday arrives at what age?

The catch is that 1900 was not a leap year, so one of his birthdays never came.

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.