50 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.