since the advent of Agriculture humans have been tracking time calendars have always been a critical part of the development of civilization they help us know when everything from meetings at work happened - what day our favorite show premieres the calendar that the world uses now is the Gregorian calendar it was a small reform of the Julian calendar which was used throughout the Roman Empire and later throughout all of medieval Europe given how the Western world has been using the same calendar for at least a thousand years we hardly even notice it anymore yet it shapes
how we think of time itself I'm Daniel C housen and this is the answer archive a strange history of the calendar the calendar is one of the longest continuous projects of humanity our calendars origin story goes all the way back to the Egyptians who are the first to adopt the 365 day year and 12-month format each month in the Egyptian calendar was divided into 30 days of course the continual frustration of all calendar makers is immediately clear 365 refuses to divide evenly and with a 30 day month 5 extra days are left over the Egyptians
solved this problem by simply having five extra days at the end of their calendar reserved for festivals and just called it good unlike the Egyptians the Romans in the days of the Republic had 12 months of varying amounts of days the same as we do today however their calendar still only added up to 355 days and the religious officials in Rome had extreme power over the links of months and years people being people the pontiff's would often use the calendar as a political tool shortening or lengthening politicians terms by literally taking and giving days this
calendar fiddling would mess with people's ability to keep the days straight and added to the issues already present in the Roman calendar not only that but the Romans were really weird in the way they actually discussed dates and day to day life anyone who has read Shakespeare's Julius Caesar knows that Caesar was assassinated on the Ides of March but what does that actually mean Romans would count their days based off three key dates in every month the calendar the nones and the Ides these three dates were used as reference points that were counted forward or
backward from in order to represent specific days The Ides would of each month and either occurred on the 15th or the 13th depending on the month the knowns were on the fifth or the seventh of each month Kalen day was on the first day of the month and that is where we get the word calendar from unfortunately the solar year isn't actually 365 days long it's 365.2422 days long this horrible number practically necessitated reform something which the Egyptians realized pretty quickly considering Ptolemy the 3rd was already recommending adding leap day every four years in 238
BC but Egyptians are nothing if not stubborn jump forward 12 Ptolemies and 200 years and Egypt still hadn't adopted the leap year until Julius Caesar's adopted son Octavian you may know him as Augustus decided enough was enough he just conquered Egypt and forced them to have a leap day every four years strangely enough though the reform that Julius Caesar made actually came from Egypt not Rome in 48 BC a Sicilian named Apollodorus entered Julius Caesar's apartment in the dead of night with a rolled-up blanket on his back once unfurled inside was a 21 year old
girl who would incidentally changed the calendar forever her name was Cleopatra she had recently been ousted from her throne by her brother and a coup and was coming to ask for Caesars help in restoring her to power needless to say Caesar was quickly seduced by her beauty and he agreed to help he ordered her brother Ptolemy the 13th to Co rule with Cleopatra and in celebration Cleopatra threw a huge party according to the Roman poet Lucan Caesar first heard of the Egyptians solar calendar from a scholar at this party and this inspired him to reform
the Roman calendar once he returned home in 46 BC Julius Caesar gathered the best living philosophers and mathematicians in order to reform the Roman lunar calendar and to an egyptian-style solar calendar ultimately they ended up just agreeing with Ptolemy the third and determined that the year should be 365 days long and every four years an extra day should be added in order to actually achieve this reform Caesar added an extra 60 in days to that year and called it the last year of confusion but everyone else just called it the year of confusion luckily for
us though they were mostly right about the length of the year and the calendar now drifted by only a single day every 134 years but for some popes a single day every 134 years isn't accurate enough before it can be understood why Pope Gregory the 13th decided to change the calendar yet again a few things have to be understood about calendar systems in general and about determining the date of Easter in particular first let's talk a bit about calendar systems there are three major kinds of calendars I've already mentioned two of them solar calendars lunar
calendars and lunisolar calendars our calendar ultimately is a solar calendar that grew out of a lunar one strangely enough that is why we even have months which at one point would have followed the cycles of the moon and even still in the Catholic Church there is a lunar calendar built into the Gregorian calendar but it only really exists to determine the date of Easter the way Easter's date is determined is boring complicated and the date will differ depending on whether you live in the Western or Eastern world to simplify the date of Easter had drifted
by over a week in Pope Gregory the 13th time and soon it would move out of spring and into summer this really annoyed the Pope and revealed the small inaccuracy present in the Julian calendar in terms of lunar calendars though the one used to decide the date of Easter and the Islamic calendar are the last vestiges of lunar calendars in our society to explain lunar calendars in short they are organized into twelve months where each month starts with the new moon and the length of the month will be either 29 or 30 days long the
year just like the old Roman calendar adds up to either 354 or 355 days of course this causes huge drifts in terms of seasons from year to year and is why Muslims observe Ramadan a month-long period of fasting in prayer at different times of the Gregorian year depending on how it lines up with the Islamic lunar calendar though the calendar is based on scientific phenomenon like the cycles of the Sun and the moon it is important to remember that the calendar is not natural at its core the calendar is a philosophical and cultural invention it
won't tell you what year month week or day it is it doesn't tell you today is May 3rd instead it just shows you when May 3rd is unless you're using Google Calendar which let's be honest you all are so even though it may have seemed insane to the Roman people or to Catholic countries in the late 1500s calendars can be changed and Pope Gregory the 13th did just that he gathered a group of genius scientists and doctors to try and create the most accurate calendar possible eventually they found a relatively elegant solution every year divisible
by 4 should be a leap year unless the year is also divisible by 100 than it is not a leap year however if that year is divisible by 400 then ignore this and it's still a leap year this reform would mean that instead of drifting by 11 minutes each year the calendar would drift by only 26 seconds in order to fix the current date though of course just like in Caesars time people would have to suffer with a day change so in every Catholic country the day after October 4th 1582 was October 15th not October
5th and also just like in Rome a millennia and a half earlier people did not like this everything from debt deadlines to holidays to birthdays were changed even the Pope's birthday changed from January 1st to January 11th mobs arose around Europe angry about their 10 lost days and mini-mini countries did not adapt to this new calendar quickly England wouldn't use the Gregorian calendar until 1752 and Greece was the last European country to hold out finally adopting it in 1923 China didn't adopt the Gregorian calendar until 1949 in a strange twist of fate though the last
major challenge that the calendar would face would not be because it wasn't accurate enough but because it was too accurate today the year is determined in the same way that the second is using an atom of caesium all atoms have oscillations that can be accurately measured and are consistent and caesium happens to have a very regular pattern of wobbles by using a cesium atom we have been able to define the year down to the nanosecond unfortunately the earth refuses to cooperate with our calendars and timekeepers every eight hundred days the earth slows its rotation by
a full second and because of that a leap second is added every few years in order to try to match the length of the day today there is a master clock in the US Naval Observatory that brings together data from 50 atomic clocks and feeds into a system that measures time around the world we've tried to make an accurate tool for measuring time that works on every single level but we are far from capable of doing so there are just too many variables at play there are many different ways of defining the year from the
side aerial to the tropical year and the Earth's slowing rotation certainly doesn't help when it comes to defining it based on equinoxes to our modern ears it may seem frightening but our year will likely always be inaccurate chances are millennia from now people will be suffering from a few skipped days or a change in the date of their birth but the fact remains that the earth the Sun in the moon don't notice or care the Sun will still rise and the earth will still orbit it the calendar has an enormous impact on our daily lives
and it's easy to just take for granted the day or the year next time you look at a calendar or check the date on your phone remember that you are looking at a calendar created by the early Egyptians reformed by Julius Caesar himself and that grew naturally out of multiple cultures and times hey guys thanks for watching before you go I've got a few people to thank as you may have noticed this time there were no interviewees but that doesn't mean that I didn't get my information from anywhere but Lily episode you'll find the links
and sources that I used and of course I'm the writer and producer of this show Daniel C Hassan and my executive producer is Josh's Cora I hope you enjoyed it and thanks for watching you
