History of Our Gregorian Calendar

Ever wonder how our calendar system came to be? With the New Year upon us, we thought this might be interesting…

History of Calendars

The oldest known calendar is a Lunar Calendar in Aberdeenshire, Scotland, believed to be from around 8,000 BCE.
In many early civilizations, calendar systems were developed. For example, in Sumer, the birthplace of the modern sexagesimal system, there were 12 months of 29 or 30 days, much like the modern Gregorian calendar.

What is a Sexagesimal System?

Sexagesimal (base 60) is a numeral system with sixty as its base. It originated with the ancient Sumerians in the 3rd millennium BC, it was passed down to the ancient Babylonians, and it is still used in a modified form for measuring time, angles, and geographic coordinates.

The number 60, a highly composite number, has twelve factors, namely {1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, 60}, of which 2, 3, and 5 are prime numbers. With so many factors, many fractions involving sexagesimal numbers are simplified.

Ancient Sumerian Calendar

The ancient Sumerian calendar divided a year into 12 lunar months of 29 or 30 days. Each month began with the sighting of a new moon. Sumerian months had no uniform name throughout Sumer because of the religious diversity. This resulted in scribes and scholars referring to them as “the first month”, “the fifth month” etc.

Sumerian Calendar

To keep the lunar year of 354 days in step with the solar year of 365.25 days an extra month was added periodically, much like a Gregorian leap year. Also, every six years the Sumerian calendar included an extra month of 62 days.

There were no weeks in the Sumerian calendar. Holy days and time off from work were usually celebrated on the first, seventh and fifteenth of each month. In addition to these holy days, there were also feast days which varied from city to city.

A day was divided into twelve hours, six daylight hours, each lasting one-sixth of the day, and six night-time hours, each lasting one-sixth of the night. This meant the length of hours varied from month to month, daylight hours being shorter in the winter and longer in the summer and vice versa.

Ancient Mayan Calendar

Mesoamerican cultures also developed their own intricate calendars; the ancient Maya had two separate years—the 260-day Sacred Round, and the 365-day Vague Year.

Of all the ancient calendar systems, the Maya and other Mesoamerican systems are the most complex. The Mayan calendar had 2 years, the 260-day Sacred Round, or tzolkin, and the 365-day Vague Year, or haab. The Mayan god Ahau’s name was associated with the 20th day of the tzolkin cycle.

Ancient Mayan Calendar

The Sacred Round of 260 days is composed of two smaller cycles: the numbers 1 through 13, coupled with 20 different day names: Imix, Ik, Akbal, Kan, Chicchan, Cimi, Manik, Lamat, Muluc, Oc, Chuen, Eb, Ben, Ix, Men, Cib, Caban, Eiznab, Cauac, and Ahau. The Sacred Round was used to determine important activities related to the gods and humans: name individuals, predict the future, decide on auspicious dates for battles, marriages, and so on.

The two cycles of 13 and 20 intermesh and are repeated without interruption: the cycle would begin with 1 Imix, then 2 Ik, then 3 Akbal and so on until the number 13 was reached, at which point the number cycle was restarted so 13 Ben would be followed by 1 Ix, 2 Men and so on. This time Imix would be numbered 8. The cycle ended after 260 days, with the last day being 13 Ahau.

The Vague Year of 365 days is similar to our modern calendar, consisting of 18 months of 20 days each, with an unlucky five-day period at the end. The Vague Year had to do primarily with the seasons and agriculture, and was based on the solar cycle. The 18 Maya months are known, in order, as: Pop, Uo, Zip, Zotz, Tzec, Xuc, Yaxkin, Mol, Chen, Yax, Zac, Ceh, Mac, Kankin, Maun, Pax, Kayab and Cumku.

Mayan god Ahau

The unlucky five-day period was known as Uayeb, and was considered a time which could hold danger, death and bad luck.

The Vague Year began with the month of Pop. The Maya 20-day month always begins with the seating of the month, followed by days numbered 1 to 19, then the seating of the following month, and so on. This ties in with the Maya notion that each month influences the next. The Maya new year would start with 1 Pop, followed by 2 Pop, all the way through to 19 Pop, followed by the seating of the month of Uo, written as 0 Uo, then 1 Uo, 2 Uo and so on.

These two cycles coincided every 52 years. The 52-year period of time was called a “bundle” and was similar to a modern day century.

Ancient Greek Calendar

The ancient Athenian calendar was a lunisolar calendar with 354 day years, consisting of twelve months of alternating length of 29 or 30 days. To keep the calendar in line with the solar year of 365.25 days, an extra, intercalary month was added in every other year. The Athenian months were called Hekatombion, Metageitnion, Boedromion, Pyanepsion, Maimakterion, Poseidon, Gamelion, Anthesterion, Elaphebolion, Munychion, Thargelion, and Skirophorion. The intercalary month usually came after Poseidon, and was called second Poseidon.

Ancient Greek Calendar

In addition to their regular, “festival” calendar, the Athenians maintained a second, political calendar . This “conciliar” calendar divided the year into “prytanies”, one for each of the “phylai”, the subdivisions of Athenian citizens. The number of phylai, and hence the number of prytanies, varied over time. Until 307 BC, there were 10 phylai. After that the number varies between 11 and 13 (usually 12). Even more confusing, while the conciliar and festival years were about the same length in the 4th century BC, such was not regularly the case earlier or later. documents dated by prytany are frequently very difficult to assign to a particular equivalent in the Gregorian calendar.

The table of Greek Olympiads, following the four-year cycles between the Olympic Games from July 1st, 776 BC, continued until the end of the 4th century AD. The Babylonian Era of Nabonassar, beginning on February 26th, 747 BC, was used by the Greeks of Alexandria. It was later known in the Middle Ages from the works of Ptolemy. Additionally there was the Macedonian Era of the Seleucids, which began with the conquest of Babylon by Seleucus Nicator in 312 BC. It became widely used in the Levant. Jews knew it as the “era of contracts”, and used it in Europe until the 15th century.

Ancient Roman Calendar

Roman dates were sometimes calculated “from the founding of the city” of Rome, or ab urbe condita (AUC). This was originally assumed to be 750 BC, although calculations by Marcus Terentius Varro in the 1st century BC determined 753 BC to be the founding date. An alternative system had become more common even by Varro’s time, whereby the Romans referred to the names of the consuls rather than the date of the year. References to the year of consulship were used in both conversation and official records. Romans from the same family often had the same praenomen, which sometimes makes it difficult to distinguish them, and there were two consuls at any one time, each of whom might sometimes hold the appointment more than once, meaning that it was (and is) necessary to be well educated in history to understand the references.

Ancient Roman Calendar

The two systems were compatible; so that the consulship of Quintus Fufius Calenus and Publius Vatinius could be determined as 707 AUC (or 47 BC), the third consulship of Caius Julius Caesar, with Marcus Aemilius Lepidus, as 708 AUC (or 46 BC), and the fourth consulship of Gaius Julius Caesar as 709 AUC (or 45 BC).

The Romans had an eight-day week, with the market-day falling every eight days. It was called a nundinum or ‘nine-day’, because it was the ancient practice to count both the first and the last day (it is unrelated to the practice of calling Easter Sunday the ‘third day’ after Good Friday).

The old Roman year had 304 days divided into 10 months, beginning on XI Kal. Maias, or April 21st. The extra months Ianuarius and Februarius had been invented as stop-gaps. Julius Caesar realized that the system had become inoperable, so he effected drastic changes in the year of his third consulship. The New Year in 709 AUC began on January 1st and ran over 365 days until December 31st. Further adjustments were made under Augustus, who introduced the concept of the “leap year” in 737 AUC (AD 4). The resultant Julian calendar remained in almost universal use in Europe until 1582.

Julian Calendar

The Julian calendar, introduced by Julius Caesar in 46 BC (708 AUC), was a reform of the Roman calendar. It took effect in 45 BC (709 AUC), shortly after the Roman conquest of Egypt. It was the predominant calendar in the Roman world, most of Europe, and in European settlements in the Americas and elsewhere, until it was refined and superseded by the Gregorian calendar. The difference in the average length of the year between Julian (365.25 days) and Gregorian (365.2425 days) is 0.002%.

The Julian calendar has a regular year of 365 days divided into 12 months, as listed in Table of months. A leap day is added to February every four years. The Julian year is, therefore, on average 365.25 days long. It was intended to approximate the tropical (solar) year. Although Greek astronomers had known, at least since Hipparchus, a century before the Julian reform, that the tropical year was a few minutes shorter than 365.25 days, the calendar did not compensate for this difference. As a result, the calendar year gained about three days every four centuries compared to observed equinox times and the seasons. This discrepancy was corrected by the Gregorian reform of 1582.

Ancient Julian Calendar

The Gregorian calendar has the same months and month lengths as the Julian calendar, but inserts leap days according to a different rule. Consequently, the Julian calendar is currently 13 days behind the Gregorian calendar; for instance, January 1st in the Julian calendar is January 14th in the Gregorian. Old Style (O.S.) and New Style (N.S.) are sometimes used with dates to indicate either whether the start of the Julian year has been adjusted to start on January 1st (N.S.) even though documents written at the time use a different start of year (O.S.), or whether a date conforms to the Julian calendar (O.S.) rather than the Gregorian (N.S.). Dual dating uses two consecutive years because of differences in the starting date of the year, or includes both the Julian and Gregorian dates.

The Julian calendar has been replaced as the civil calendar by the Gregorian calendar in all countries which formerly used it, although it continued to be the civil calendar of some countries into the 20th century. Among the last countries to convert to the Gregorian Calendar were Greece (in 1924), Turkey (in 1926) and Egypt (in 1928). As of 1930, all countries that were using the Julian calendar had discontinued it.

Ancient Alexandrian Calendar

Most Christian denominations in the West and areas evangelized by Western churches have also replaced the Julian calendar with the Gregorian as the basis for their liturgical calendars. However, most branches of the Eastern Orthodox Church still use the Julian calendar for calculating the dates of moveable feasts, including Easter (Pascha). Some Orthodox churches have adopted the Revised Julian calendar for the observance of fixed feasts, while other Orthodox churches retain the Julian calendar for all purposes. The Julian calendar is still used by the Berber people of North Africa, and on Mount Athos.

In the form of the Alexandrian calendar, it is the basis for the Ethiopian calendar, which is the civil calendar of Ethiopia.

Hindu Calendar

The epoch (starting point or first day of the zeroth year) of the current era of Hindu calendar (both solar and lunisolar) is February 18, 3102 BC in the proleptic Julian calendar or January 23, 3102 BC in the proleptic Gregorian calendar. According to the Purāṇa-s this was the moment when Śrī Kṛṣṇa returned to his eternal abode.

Hindu Calendar

Both the solar and lunisolar calendars started on this date. After that, each year is labeled by the number of years elapsed since the epoch.

This is an unusual feature of the Hindu calendar. Most systems use the current ordinal number of the year as the year label. But just as a person’s true age is measured by the number of years that have elapsed starting from the date of the person’s birth, the Hindu calendar measures the number of years elapsed. As of August 31, 2014, 5116 years have elapsed in the Hindu calendar.

However, the lunisolar calendar year usually starts earlier than the solar calendar year, so the exact year will not begin on the same day every year.

Viking Calendar

In medieval Scandinavia, there were two seasons: summer and winter. There were twelve lunar months in the Old Icelandic lunar calendar: Harpa (“Harpa-month”), Stekktíd (“Lamb-fold-time”), Sólmánuður (“Sun-month”), Miðsumar (“Midsummer”), Heyannir (“Hay-month”), Haustmábuður (“Harvest-month”), Gormánuður (“Slaughtering-month”), Ýlir (“Ylir”), Hrútmánaður (“Ram-month”), Þorri (“Thorri-month”), Góa (“Goa-month”) and Einmánuður (“Last month of Winter”). The early days of summer (sumarmál) began in the modern month of April, and summer lasted until October. The first month of summer, Harpa, roughly corresponds to April-May.

Ancient Viking Calendar

The local “Spring Assembly”, or vorþing, took place at the end of the fourth week of summer; lasting four to seven days between 7 and 27 May. The Althing, or national parliament, was held when eight weeks of summer had passed. Lastly, the Autumn Meeting took place no later than ten weeks before the end of summer.

“Winter” lasted from October to April. The two-day period when winter began, the Winter Nights or veturnætur, occurred around the middle of October. It was a particularly holy time of the year, when sacrifices were made to the local guardian spirits and other social events such as games meetings and weddings took place. The first month of winter, Gormánuður, was also the time when animals were slaughtered so that their meat could be stored for the winter.

Anno Domini

For the first six centuries since the birth of Jesus Christ, European countries used various local systems to count years, most usually regnal years, modeled on the Old Testament. In some cases, Creation dating was also used.

Anno Domini

In the 6th century, the Christian monk Dionysius Exiguus devised the Anno Domini system, dating from the Incarnation of Jesus.

In the 8th century, the Anglo-Saxon historian Bede the Venerable used another Latin term, “ante uero incarnationis dominicae tempus” (“the time before the Lord’s true incarnation”, equivalent to the English “before Christ”), to identify years before the first year of this era.

According to the Catholic Encyclopedia, even Popes continued to date documents according to regnal years, and usage of AD only gradually became common in Europe from the 11th to the 14th centuries.

In 1422, Portugal became the last Western European country to adopt the Anno Domini system.

Christian Europe

In 1267, the medieval scientist Roger Bacon stated the times of full moons as a number of hours, minutes, seconds, thirds, and fourths (horae, minuta, secunda, tertia, and quarta) after noon on specified calendar dates. Although a third for ¹⁄₆₀ of a second remains in some languages, for example Polish tercja the modern second is further divided decimally.

Rival calendar eras to Anno Domini remained in use in Christian Europe. In Spain, the “Era of the Caesars” was dated from Octavian’s conquest of Iberia in 39 BC. It was adopted by the Visigoths and remained in use in Catalonia until 1180, Castille until 1382 and Portugal until 1415.

Old Christian Europe painting

For chronological purposes, the flaw of the Annon Domini system was that dates have to be reckoned backwards or forwards accordingly as they are BC or AD. According to the Catholic Encyclopedia, “in an ideally perfect system all events would be reckoned in one sequence. The difficulty was to find a starting point whence to reckon, for the beginnings of history in which this should naturally be placed are those of which chronologically we know least.” For both Christians and Jews, the prime historical date was the Year of Creation, or Annus Mundi. The Byzantine Church fixed the date of Creation at 5509 BC. This remained the basis of the ecclesiastical calendar in the Greek and Russian Orthodox world until modern times. The Coptic Church fixed on 5500 BC. Later, the Church of England, under Archbishop Ussher in 1650, would pick 4004 BC. Jewish scholars preferred 3761 BC as the date of creation, which forms the basis of the modern Jewish calendar. However, “any attempt thus to determine the age of the world has been long since abandoned.

Gregorian Calendar

The Gregorian calendar, also called the Western calendar and the Christian calendar, is internationally the most widely used civil calendar. It is named for Pope Gregory XIII, who introduced it in 1582.

The calendar was a refinement in 1582 to the Julian calendar amounting to a 0.002% correction in the length of the year. The motivation for the reform was to bring the date for the celebration of Easter to the time of the year in which the First Council of Nicaea had agreed upon in 325. Because the celebration of Easter was tied to the spring equinox, the Roman Catholic Church considered this steady drift in the date of Easter undesirable. The reform was adopted initially by the Catholic countries of Europe. Protestants and Eastern Orthodox countries continued to use the traditional Julian calendar and adopted the Gregorian reform after a time, for the sake of convenience in international trade. The last European country to adopt the reform was Greece, in 1923, although the last country in the world to fully convert was the Soviet Union in 1929, and as of 1930, all countries that had used the Julian calendar had discontinued it.

The Gregorian reform contained two parts: a reform of the Julian calendar as used prior to Pope Gregory XIII’s time and a reform of the lunar cycle used by the Church, with the Julian calendar, to calculate the date of Easter. The reform was a modification of a proposal made by Aloysius Lilius His proposal included reducing the number of leap years in four centuries from 100 to 97, by making 3 out of 4 centurial years common instead of leap years. Lilius also produced an original and practical scheme for adjusting the epacts of the moon when calculating the annual date of Easter, solving a long-standing obstacle to calendar reform.

The Gregorian reform modified the Julian calendar’s scheme of leap years as follows:

Every year that is exactly divisible by four is a leap year, except for years that are exactly divisible by 100, but these centurial years are leap years if they are exactly divisible by 400. For example, the years 1700, 1800, and 1900 are not leap years, but the year 2000 is.

2015 Calendar

In addition to the change in the mean length of the calendar year from 365.25 days (365 days 6 hours) to 365.2425 days (365 days 5 hours 49 minutes 12 seconds), a reduction of 10 minutes 48 seconds per year, the Gregorian calendar reform also dealt with the accumulated difference between these lengths. Between AD 325 (when the First Council of Nicaea was held, and the vernal equinox occurred approximately March 21st), and the time of Pope Gregory in 1582, the vernal equinox had moved backward in the calendar, so that in 1582 it occurred about March 11th, 10 days earlier than March 21st. The Gregorian calendar therefore began by skipping 10 calendar days, to restore March 21st as the date of the vernal equinox.

To unambiguously specify the date, dual dating or Old Style (O.S.) and New Style (N.S.) are sometimes used with dates. Dual dating uses two consecutive years because of differences in the starting date of the year, or includes both the Julian and Gregorian dates. Old Style and New Style (N.S.) indicate either whether the start of the Julian year has been adjusted to start on 1 January (N.S.) even though documents written at the time use a different start of year (O.S.), or whether a date conforms to the Julian calendar (O.S.) rather than the Gregorian (N.S.).

The Gregorian calendar continued to use the previous calendar era (year-numbering system), which counts years from the traditional date of the nativity (Anno Domini), originally calculated in the 6th century by Dionysius Exiguus. This year-numbering system, also known as Dionysian era or Common Era, is the predominant international standard today.

This unofficial history of our modern day Gregorian calendar is brought to you by Scrub-n-Shine.com.