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EVOLUTION OF CALENDARS

S. Khalid Shaukat (January 2014)

Ancient Calendars: All ancient calendars were lunar calendars. The practice of starting a month at the first sighting of a new moon was observed not only by Romans but by Celts and Germans in Europe and by Babylonians and Hebrews in the Lavant. The new moons were sighted after either 29 or 30 days. If clouds obscured vision on the 29th day, that month was declared to have 30 days. This is still done for the Islamic Calendar.

When human civilization excelled in agriculture, there was a need for having a calendar that repeats the seasons so that it would help sowing and harvesting on repeated calendar dates. This calendar was established based on rotation of the earth around the sun. Early estimates of this rotation was 360 days, so the first solar calendar was invented having 12 months of 30 days each. Some civilizations invented a lunisolar calendar which basically had lunar months based on new crescent moons but were adding days or a month to be decided by priests/rabiis wherever and whenever they felt to satisfy social and religious needs to keep their calendar in phase with seasons. This practice of adding days or a 13th month was called "Intercalation".

Babylonian Calendar: Around 1800 B.C. Babylonians were using strictly lunar calendar based on the visible new crescent but somewhere between 1100 B.C and 800 B.C. a lunisolar calendar was adopted using intercalation which was haphazard. Some sources report that during the reign of the Babylonian king Nebuchadenezzar II (630 B.C. - 562 B.C.) priest/experts discontinued their practice of looking for the new moon and adopted a 365 day calendar of 12 months of 30 days each, with five days added at the end of the year.

Hindu Calendar: Hindus have both solar and lunisolar calendars. In the Hindu solar calendar month is 30 or 31 days and begins on the day of first sunrise after the calculated time of the mean sun's entry into the next zodiacal sign. If the calculated time is after midnight but before (or at) sunrise, then the day of entry is the first day of the new month; otherwise it is the last day of the previous month. In the Hindu lunisolar system months follow the lunar cycle and are synchronized with the solar year by introducing occasional leap months. In south-India months begin at new moon while in north-India months begin at full moon.

Chinese Calendar: Chinese also started using a lunisolar calendar with months beginning on the day of the new moon. Years contain 12 or 13 such months , with the number of months determined by the number of new moons between successive winter solstices. There have been more than 50 calendar reforms since its inception in the 14th century B.C.

Egyptian Calendar: In order to device a solar calendar in ancient times experts observed that Sirius, brightest of all the fixed stars, appeared in summer, rising above horizon just before sunrise. They also noticed that Sirius would return to its position after 365 days. Thus, Egyptians deviced a solar calendar built around 365 days. They gave up their practice of looking for the new moon in favor of the solar calendar.

Greek Calendar: By 13th century B.C. Greeks were using lunar calendar based on the visible new crescent. Later they also learnt intercalation to bring lunar calendar in phase with seasons and started using lunisolar calendar. Astronomers such as Maton in 432 B.C. calculated a 19-year lunisolar cycle where moon phases would repeat in the same seasons. This was called "Metonic Cycle" where 19 solar years were equal to lunar 19 years and 7 months. This concept was later adopted by Jewish or Hebrew calendar.

Hebrew Calendar: Hebrew Calendar, promulgated by the Patriarch, Hillel II, in the mid-fourth century is a lunisolar calndar with months based on new crescent moon but adding a 13th month every so often to bring their lunisolar calendar in phase with the seasons. It consists of 12 month in a common year and 13 months in a leap year. Leap years occur seven times in a cycle of 19 years (Metonic cycle), such that 3rd, 6th, 8th, 11th, 14th, 17th, and 19th year are leap years. Common years may have 353-355 days, while leap years may have 383-385 days. The beginning of the Hebrew new year is determined by the occurrence of the new moon (conjunction) of the seventh month (Tishri), subject to possible postponement of a day or two according to some rules.

Roman Calendar: About seven hundred years before Julius Caeser, Romans were observing some nominally lunar calendar, and were adding days or a 13th month at the end of their calendar year to keep their calendar in phase with seasons.

Roman Calendar before 47 B.C. [Used Intercalation of days or a 13th month]
Number 1234 5678 9101112
Month MartiusApriliusMaiusJunius QuintilisSextilisSeptemberOctober NovemberDecemberJanuariusFebruarius
Days 29 or 3029 or 3029 or 3029 or 30 29 or 3029 or 3029 or 3029 or 30 29 or 3029 or 3029 or 3029 or 30
The new year used to begin on March 15, which was the date when new consul took office. In 153 B.C. the beginning of the year was changed to January 1. This was carried over into the Julian calendar.

Julian Calendar: Following his conquest of Egypt in 48 B.C. Roman Emperor, Julius Caeser consulted the Alexandrian astronomer Sosigenes about calendar reform. Caeser adopted the calendar identical to the Alexandrian Aristarchus' calendar of 239 B.C., that consisted of a solar year of 12 months and of 365 days with an extra day every fourth year. This was a truly solar calendar and was later called, "Julian Calendar" named after him. Month lengths were extended to 30 or 31 for different months to bring the calendar's total to 365 with an addition of an extra day every fourth (leap) year to account for the true length of the solar year more close to 365.25 days.

By the year 46 B.C. it was noticed that the spring equinox had shifted by about 2 months coming in May. Caeser wanted to bring spring equinox into correct position of Martius (March) 21. The year 46 B.C. is regarded as the "year of confusion" by modern authors, because in that year two intercalations were done; one to correct for spring equinox and the other to change lunisolar calendar to purely solar calendar resulting in the length of that year to 445 days. The following year i.e., 45 B.C. the Julian Calendar looked like this:

Julian Calendar (of Julius Caeser), 45 B.C. onwards
Number 1234 5678 9101112
Month JanuaryFebruaryMarchApril MayJuneQuintilisSextilis SeptemberOctoberNovemberDecember
Days 3130(Leap) 29(Non-leap)3130 31303130 31303130

Caeser was assassinated in 44 B.C. and the month Quintilis was later renamed as Julius (July) to honor him. Soon after Caesar's assassination, his nephew and adopted son Octavian became the emperor that we refer to as "Augustus," an honorary title that had been bestowed upon him. For a time after his death, priests in charge of the calendar erroneously inserted an extra day every three years instead of every four. As a result, this caused the calendar to again drift away from the seasons, an error that needed correction. In 8 A.D. Octavian found it necessary to readjust the calendar. To eliminate the effect of this extra intercalation, leap years were discontinued from about 9 B.C. until 8AD. The leap years were:

45BC, 42BC, 39BC, 36BC, 33BC, 30BC, 27BC, 24BC, 21BC, 18BC, 15BC, 12BC, 9BC, 8AD, 12AD and every 4th year from then on.

To reward him for his accomplishments, the Roman Senate voted to name a month in his honor, just as the month of Quintilis had previously been named Julius (July) after the first Caesar. Because Octavian had been born in Septembris, they offered to rename that month for him. He chose Sextilis instead, because several times he had been fortunate during that month. But the way the story goes, Sextilis in Octavian's time had only 30 days. Octavian's advisors suggested that the month named after him should not be deficient compared to Julius's month of 31 days. Octavian (Augustus) thus looked around for a month from which he could remove a day. Romans had religious festivals that were held on specific days of each month; it would have been difficult for him to delete any day that remembered a revered event, so he took a day from Februarius which was already an odd month and added it to Sextilis, which was then renamed Augustus (August). So February now had only 28 days in common years but had 29 in leap years.

If Octavian had made no further changes, July, August and September, three consecutive months, would then all have had 31 days. In order to prevent a string of three 31 day months in a row, he removed one day each from September and November and added one day to both October and December. As a result, there are now only two 31-day months in succession in the middle of the year (July and August) and two at the turn of the year (December and January). Others claim that lengthening the month of Sextilis and renaming it Augustus was done not by Octavian but by the consuls Asinius Gallus and Marcius Censorinus who served as Ordinary Consuls of the Roman Republic in 8 A.D.

Julian Calendar (of Augustus), 8 A.D. onwards
Number 1234 5678 9101112
Month JanuaryFebruaryMarchApril MayJuneJulyAugust SeptemberOctoberNovemberDecember
Days 3129(Leap) 28(Non-leap)3130 31303131 30313031

As time progressed, the church did not like the idea of January 1 being the new year, and in 567 A.D. the council of Tours declared that year start should be reverted back to March. They used March 25 as the beginning of the year. This practice continued until Gregorian reform in 1582 A.D.

Gregorian Calendar: The prevailing Julian calendar served well for a long time. However, adding an extra day every four years resulted in extending the calendar over eleven minutes beyond the seasons every year. This was not perceived as a problem for hundreds of years, but by the middle of the sixteenth century of this Common Era, these added minutes had accumulated to ten days. As a result, religious festivals were being observed on the wrong date as compared with their original seasons. This problem had been known and discussed for several centuries, but was not completely corrected until near the end of the sixteenth century (1582 A.D.) at the time of Pope Gregory XIII resulting in present Gregorian Calendar. Pope Gregory XIII decreed that after October 4, 1582 (Thursday) ten days will be dropped making the next day October 15, 1582 (Friday). At the same time the beginning of the year was also brought back from March 25 to January 1, as in the beginning of Julian Calendar of Julius Caeser. The rule for the leap years was changed. In the Julian Calendar a year is leap if it is divisible by 4. In the Gregorian Calendar a year is leap if either (i)it is divisible by 4 but not by 100 or (ii) it is divisible by 400.

Gregorian Calendar, 1583 A.D. onwards [Only the leap year treatment was modified]
Number 1234 5678 9101112
Month JanuaryFebruaryMarchApril MayJuneJulyAugust SeptemberOctoberNovemberDecember
Days 3129(Leap) 28(Non-leap)3130 31303131 30313031

This Gregorian correction was adopted by Italy, Poland, Portugal, and Spain. Most other Catholic countries followed shortly after. Great Britain (including what is now USA) adopted in 1752, such that Sep 2, 1752 was followed by Sep 14, 1752. Russia adopted in 1918, such that Jan 31, 1918 was followed by Feb 14, 1918. In Turkey, Gregorian calendar was introduced on Jan 1, 1927.

The 13 Month calendar: (also known as The International Fixed calendar or the Equal Month calendar) is a solar calendar proposal for calendar reform designed by Moses B. Cotsworth, who presented it in 1902. It provides for a year of 13 months of 28 days each, with one or two days a year belonging to no month or week. It is therefore a perennial calendar, with every date fixed always on the same weekday.

13 Months Calendar, Proposed in 1902 A.D.
SundayMondayTuesdayWednesdayThursdayFridaySaturday
1234567
891011121314
15161718192021
22232425262728

The calendar year has 13 months with 28 days each, divided into exactly 4 weeks [(13 * 28) = 364]. An extra day added as a holiday at the end of the year, sometimes called "Year Day," brings the total to 365 days. In Leap years, another extra day added as another holiday at the end of the year, sometimes called "Leap Year Day," brings the total to 366 days. Each year coincides with the corresponding Gregorian year, so January 1 in the 13 Months Calendar always falls on Gregorian January 1. Twelve months are named and ordered the same as those of the Gregorian calendar, except that the extra month is inserted between June and July, and called Sol. Situated in mid-summer (from the point of view of its Northern Hemisphere authors), the name of the new month was chosen in homage to the sun. Order of months would be as follows:

JanuaryFrbruaryMarchAprilMayJuneSolJulyAugustSeptemberOctoberNiovemberDecember 

This 13 Months Calendar was never officially adopted in any country or any world organization, mainly because the 2 extra days (Year Day and Leap Year Day) are not assigned any week day, and a continuous count of 7 days a week will be disturbed.

The World Calendar: is a proposed reform of the Gregorian calendar created by Elisabeth Achelis of Brooklyn, New York in 1930, for The World Calendar Association.

The World Calendar is a 12-month, with equal quarters. It is perennial, or perpetual, because it remains the same every year. Each quarter begins on Sunday, ends on Saturday. The quarters are equal: each has exactly 91 days, 13 weeks or 3 months. The three months have 31, 30, 30 days respectively. Each quarter begins with the 31-day months of January, April, July, or October. The World Calendar also has the following two additional days to maintain the same new year days as the [Gregorian calendar].

One is named Worldsday which is the last day of the year following Saturday 30 December. This additional day is dated "W", which equals 31 December, and it will be a year-end world holiday. It is followed by Sunday, 1 January in the new year. The other is named Leapyear Day, which is similarly added at the end of the second quarter in [leap years]. It is also dated "L", which equals 31 June, and named Leapyear Day. It is followed by Sunday, 1 July within the same year. The World Calendar treats Worldsday and Leapyear Day as a 24-hour waiting period before resuming the calendar again. These off-calendar days are not assigned weekday designations. They are intended to be treated as holidays.

The World Calendar, Proposed in 1932 A.D.
January
SuMoTuWeThFrSa
1234567
891011121314
15161718192021
22232425262728
293031    
February
SuMoTuWeThFrSa
   1234
567891011
12131415161718
19202122232425
2627282030  
March
SuMoTuWeThFrSa
     12
3456789
10111213141516
17181920212223
24252627282930
April
SuMoTuWeThFrSa
1234567
891011121314
15161718192021
22232425262728
293031    
May
SuMoTuWeThFrSa
   1234
567891011
12131415161718
19202122232425
2627282030  
June
SuMoTuWeThFrSa
     12
3456789
10111213141516
17181920212223
24252627282930
July
SuMoTuWeThFrSa
1234567
891011121314
15161718192021
22232425262728
293031    
August
SuMoTuWeThFrSa
   1234
567891011
12131415161718
19202122232425
2627282030  
September
SuMoTuWeThFrSa
     12
3456789
10111213141516
17181920212223
24252627282930
October
SuMoTuWeThFrSa
1234567
891011121314
15161718192021
22232425262728
293031    
November
SuMoTuWeThFrSa
   1234
567891011
12131415161718
19202122232425
2627282030  
December
SuMoTuWeThFrSa
     12
3456789
10111213141516
17181920212223
24252627282930

This World Calendar was never adopted by any country or any world organization, mainly because the 2 extra days (Worldsday and Leapyear Day) are not assigned any week day, and a continuous count of 7 days a week will be disturbed.

Bibliography:

1. "Encyclopedia Britannica"

2. "Calendrical Calculations: The Millenium Edition," Reingold, E.M., and Dershowitz, N., Cambridge University Press, December 1999.

3. "Chronology of the Ancient World," Bickerman, E.J., Cornell University Press, Ithaca, NY, 1968.

4. "Calendars," Doggett, L.E., University Science Books, Sausalito CA 94965