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A Variety of Calendars

Today almost everyone takes the precision of our calendars for granted, unaware of the long threads spooling out from our clocks and watches backward in time, running through virtually every major revolution in human science, all linked to the measurement of time. The thread runs largely through the West, since this is the source of the world’s civic calendar, but also casts lines of varying sizes and thickness outward to China, India, Egypt, Arabia, and Mesopotamia.

Unwinding backward, it pauses at Clavious and at Bacon; at the rush of knowledge coming from Islam and the East during the Middle Ages; at bloody wars fought over dates after Rome’s collapse; and at Rome at its height, when Julius Caesar fell in love with Cleopatra, an affair that gave the west its calendar.

It moves back farther still to the Egypt of the pharaohs, Babylon, Sumer, and beyond, thousands of years before our own calendar was created, when an unknown person dressed in reindeer skins and clutching an eagle bone gazed at the sky and got an idea to use the moon to measure time.

Many different calendars have been developed over the millennia to help people organize their lives. According to a recent estimate, there are about forty calendars used in the world today, particularly for determining religious dates. Most modern countries use the Gregorian calendar (see the Year) for their official activities.

Westerners should keep in mind that there are indeed several calendars actively in use. For example, there are 11 public holidays in Singapore:
  • New Year’s Day (January 1)
  • Chinese New Year and day after.
  • Good Friday
  • Labor Day (May 1)
  • Vesak Day
  • National Day (August 9)
  • Deepavali
  • Christmas (December 25)
  • Hari Raya Puasa
  • Hari Raya Haji
These include three secular holidays, New Year’s Day, Labor Day and National Day, and eight religious/cultural holidays (two Chinese, two Islamic, two Indian and two Christian). Christmas falls on a fixed date in the Gregorian calendar, but the other seven traditional holiday are movable.

Indian Calender

As a result of a calendar reform in 1957 C.E., the National Calendar of India is a formalized lunisolar calendar in which leap years coincide with those of the Gregorian calendar (Calendar Reform Committee, 1957). However, the initial epoch is the Saka Era, a traditional epoch of Indian chronology. Months are named after the traditional Indian months and are offset from the beginning of Gregorian months (see the table below).

In addition to establishing a civil calendar, the Calendar Reform Committee set guidelines for religious calendars, which require calculations of the motions of the Sun and Moon. Tabulations of the religious holidays are prepared by the India Meteorological Department and published annually in The Indian Astronomical Ephemeris.

Despite the attempt to establish a unified calendar for all of India, many local variations exist. The Gregorian calendar continues in use for administrative purposes, and holidays are still determined according to regional, religious, and ethnic traditions.

Months of the Indian Civil CalendarDaysCorrelation of Indian/Gregorian
1. Caitra30*Caitra 1March 22*
2. Vaisakha31Vaisakha 1April 21
3. Jyaistha31Jyaistha 1May 22
4. Asadha31Asadha 1June 22
5. Sravana31Sravana 1July 23
6. Bhadra31Bhadra 1August 23
7. Asvina30Asvina 1September 23
8. Kartika30Kartika 1October 23
9. Agrahayana30Agrahayana 1November 22
10. Pausa30Pausa 1December 22
11. Magha30Magha 1January 21
12. Phalguna30Phalguna 1February 20
* In a leap year, Caitra has 31 days and Caitra 1 coincides with March 21.

History of the Indian calendar

The history of calendars in India is a remarkably complex subject owing to the continuity of Indian civilization and to the diversity of cultural influences. In the mid-1950s, when the Calendar Reform Committee made its survey, there were about 30 calendars in use for setting religious festivals for Hindus, Buddhists, and Jainists.

Some of these were also used for civil dating. These calendars were based on common principles, though they had local characteristics determined by long-established customs and the astronomical practices of local calendar makers. In addition, Muslims in India used the Islamic calendar, and the Indian government used the Gregorian calendar for administrative purposes.

Early allusions to a lunisolar calendar with intercalated months are found in the hymns from the Rig Veda, dating from the second millennium B.C.E. Literature from 1300 B.C.E. to C.E. 300, provides information of a more specific nature. A five-year lunisolar calendar coordinated solar years with synodic and sidereal lunar months.

Indian astronomy underwent a general reform in the first few centuries C.E., as advances in Babylonian and Greek astronomy became known. New astronomical constants and models for the motion of the Moon and Sun were adapted to traditional calendric practices. This was conveyed in astronomical treatises of this period known as Siddhantas, many of which have not survived. The Surya Siddhanta, which originated in the fourth century but was updated over the following centuries, influenced Indian calendrics up to and even after the calendar reform of C.E. 1957.

The author Pingree provides a survey of the development of mathematical astronomy in India. Although he does not deal explicitly with calendrics, this material is necessary for a full understanding of the history of India’s calendars.

Chinese Calendar

Chinese New Year is the main holiday of the year for more than one quarter of the world’s population. Although the People’s Republic of China uses the Gregorian calendar for civil purposes, a special Chinese calendar is used for determining festivals. Various Chinese communities around the world also use this calendar.

The beginnings of the Chinese calendar can be traced back to the 14th century B.C.E. Legend has it that the Emperor Huangdi invented the calendar in 2637 B.C.E.

The Chinese calendar is based on exact astronomical observations of the longitude of the sun and the phases of the moon. This means that principles of modern science have had an impact on the Chinese calendar.

Unlike most other calendars, the Chinese calendar does not count years in an infinite sequence. Instead years have names that are repeated every 60 years.

(Historically, years used to be counted since the accession of an emperor, but this was abolished after the 1911 revolution.)

Within each 60-year cycle, each year is assigned name consisting of two components:

The first component is a Celestial Stemm. These words have no English equivalent:


The second component is a Terrestrial Branch. The names of the corresponding animals in the zodiac cycle of 12 animals are given in parentheses.

1zi (rat)7wu (horse)
2chou (ox)8wei (sheep)
3yin (tiger)9shen (monkey)
4mao (hare, rabbit)10you (rooster)
5chen (dragon)11xu (dog)
6si (snake)12hai (pig)

Chinese yearZodiac animalGregorian calendar
4693BoarJanuary 31, 1995
4694RatFebruary 19, 1996
4695OxFebruary 7, 1997
4696TigerJanuary 28, 1998
4697Hare/RabbitFebruary 16, 1999
4698DragonFebruary 5, 2000
4699SnakeJanuary 24, 2001
4700HorseFebruary 12, 2002
4701Ram/SheepFebruary 1, 2003
4702MonkeyJanuary 22, 2004
4703RoosterFebruary 9, 2005
4704DogJanuary 29, 2006
4705BoarFebruary 18, 2007
4706RatFebruary 7, 2008
4707OxJanuary 26, 2009
4708TigerFebruary 10, 2010
4709Hare/RabbitFebruary 3, 2011
4710DragonJanuary 23, 2012
4711SnakeFebruary 10, 2013
4712HorseJanuary 31, 2014
4713Ram/SheepFebruary 19, 2015
4714MonkeyFebruary 9, 2016
4715RoosterJanuary 28, 2017
4716DogFebruary 16, 2018
4717BoarFebruary 5, 2019
4718RatJanuary 25, 2020

Islamic calendar

The Islamic calendar (or Hijri calendar) is a purely lunar calendar. It contains 12 months that are based on the motion of the moon, and because 12 synodic months is only 12 x 29.53=354.36 days, the Islamic calendar is consistently shorter than a tropical year, and therefore it shifts with respect to the Christian calendar.

The calendar is based on the Qur'an (Sura IX, 36-37) and its proper observance is a sacred duty for Muslims.

The Islamic calendar is the official calendar in countries around the Gulf, especially Saudi Arabia. But other Muslim countries use the Gregorian calendar for civil purposes and only turn to the Islamic calendar for religious purposes.

The names of the 12 months that comprise the Islamic year are:

1. Muharram7. Rajab
2. Safar8. Sha'ban
3. Rabi’ al-awwal (Rabi’ I)9. Ramadan
4. Rabi’ al-thani (Rabi’ II)10. Shawwal
5. Jumada al-awwal (Jumada I)11. Dhu al-Qi'dah
6. Jumada al-thani (Jumada II)12. Dhu al-Hijjah

(Due to different transliterations of the Arabic alphabet, other spellings of the months are possible.)
Each month starts when the lunar crescent is first seen (by a human observer’s eye) after a new moon.

Although new moons may be calculated quite precisely, the actual visibility of the crescent is much more difficult to predict. It depends on factors such as weather, the optical properties of the atmosphere, and the location of the observer. It is therefore very difficult to give accurate information in advance about when a new month will start.

Furthermore, some Muslims depend on a local sighting of the moon, whereas others depend on a sighting by authorities somewhere in the Muslim world. Both are valid Islamic practices, but they may lead to different starting days for the months.

Mayan Calendar

Among their other accomplishments, the ancient Mayas invented a calendar of remarkable accuracy and complexity.

The Pyramid of Kukulkan at Chichén Itzá, constructed circa 1050 was built during the late Mayan period, when Toltecs from Tula became politically powerful. The pyramid was used as a calendar: four stairways, each with 91 steps and a platform at the top, making a total of 365, equivalent to the number of days in a calendar year.

The Maya calendar was adopted by the other Mesoamerican nations, such as the Aztecs and the Toltec, which adopted the mechanics of the calendar unaltered but changed the names of the days of the week and the months.

The Maya calendar uses three different dating systems in parallel, the Long Count, the Tzolkin (divine calendar), and the Haab (civil calendar). Of these, only the Haab has a direct relationship to the length of the year.

A typical Mayan date looks like this:, 3 Cimi 4 Zotz. is the Long Count date.
3 Cimi is the Tzolkin date.
4 Zotz is the Haab date.

The names of the month were:

1. Pop7. Yaxkin13. Mac
2. Uo8. Mol14. Kankin
3. Zip9. Chen15. Muan
4. Zotz10. Yax16. Pax
5. Tzec11. Zac17. Kayab
6. Xul12. Ceh18. Cumku



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