The Burmese chronicles trace the origin of the Burmese calendar to ancient India with the introduction of the Kali Yuga Era in 3102 BCE. That seminal calendar is said to have been recalibrated by King Añjana (အဉ္စန), the maternal grandfather of the Buddha, in 691 BCE. That calendar in turn was recalibrated and replaced by the Buddhist Era with the starting year of 544 BCE. The Buddhist Era came to be adopted in the early Pyu city-states by the beginning of the Common Era. Then in 78 CE, a new era called the Shalivahana era, also called Sakra Era or Saka Era, was launched in India. Two years later the new era was adopted in the Pyu state of Sri Ksetra, and the era later spread to the rest of the Pyu states.
According to the chronicles, the Pagan Kingdom at first followed the prevailing Saka Pyu Era, but in 640 CE King Popa Sawrahan (r. 613–640) recalibrated the calendar, naming the new era Kawza Thekkarit (ကောဇာ သက္ကရာဇ် [kɔ́zà θɛʔkəɹɪʔ]) with a Year Zero starting date of 22 March 638 CE. It was used as the civil calendar, while the Buddhist Era remained in use as the religious calendar.
Scholarship accepts the chronicle narrative regarding the North Indian origin of the calendar and the chronology of adoption in Burma up to the Mahāsakaraj Era. Recent research suggests that the Gupta Era (epochal year of 320 CE) may also have been in use in the Pyu states.[note 1] Mainstream scholarship, however, holds that the recalibrated calendar was launched at Sri Ksetra, and later adopted by the upstart principality of Pagan.
The adoption by an ascendant Pagan paved the way for the calendar's adoption elsewhere in the Pagan Empire between the 11th and 13th centuries. The calendar first came to be used in peripheral regions or neighbouring states such as Arakan in the west and various Shan states in modern northern Thailand and Laos in the east, which adopted the calendar alongside folklore connected with the Burmese New Year. According to the Chiang Mai Chronicles and the Chaing Saen Chronicles, Chiang Mai and Chiang Saen and their tributary states of middle and upper Tai country (except Lamphun and Sukhothai) submitted to King Anawrahta and adopted the calendar in the mid-11th century in place of Mahāsakaraj, the standard calendar of the Khmer Empire.[note 2] However, scholarship says the earliest evidence of Burmese calendar in modern Thailand dates only to the mid-13th century.
While the use of the calendar appears to have spread southward to Sukhothai and eastward to Laotian states in the following centuries, the official adoption farther south by the Ayutthaya Kingdom and farther east by Lan Xang came only after King Bayinnaung's conquests of those kingdoms in the 16th century. Subsequent Siamese kingdoms retained the Burmese calendar as the official calendar under the name of Chulasakarat (Pali: Culāsakaraj) until 1889. The Siamese adoption turned out to be the main catalyst for the calendar's usage in Cambodia, a periodic vassal of Siam between the 16th and 19th centuries. Likewise, the calendar spread to the Chittagong region of Bengal, which was dominated by the Arakanese Mrauk-U Kingdom from the 15th to 17th centuries.
Development and changes
The calculation system of the Burmese calendar was originally based on Thuriya Theiddanta (သူရိယသိဒ္ဓန္တ [θùɹḭja̰ θeiʔdàɴta̰], which is believed to be chiefly based on the "original" Surya Siddhanta system of ancient India (i.e. Ardharatrika school). One key difference from Indian systems was that the Burmese system followed a 19-year intercalation schedule (Metonic cycle). It is unclear from where, when or how the Metonic system was introduced; hypotheses range from China to Europe.[note 3]
The Burmese system thus uses a "strange" combination of sidereal years from the Indian calendar with the Metonic cycle, which is better for tropical years than sidereal years, so necessitating intercalation adjustments to reconcile the differences. Furthermore, the Burmese system did not incorporate advances in Indian calculation methods of the sidereal year until the mid-19th century.[note 4] (The original Thuriya Theiddanta system is 0.56 second a year slower (and more accurate) than later Indian systems.)
The earliest attempts on record to change the calendar were superficial. On the 800th anniversary of the calendar (29 March 1438), King Mohnyin Thado recalibrated the calendar to Year 2 (with Year Zero beginning on 18 March 1436). But the king died just over a year after the launch, and the new era died out a few years later. The next proposed change came in March 1638 from King Prasat Thong of Siam who in preparation of the upcoming millennial anniversary (10 April 1638) wanted to make a change to the governing animals of the months. As the practice was not prevalent in Burma, the proposal was rejected by King Thalun.
Meanwhile, the growing cumulative discrepancy between the civil solar and luni-solar years attracted increasing attention. In the 1100th anniversary year (1738 CE) a new system of calculation was proposed that aimed to correct the errors of the original system, but the Toungoo court did not take any action. The present Surya Siddhanta (i.e., Saura school) was introduced to the Konbaung court in 1786, and was translated into Burmese after about 50 years. Finally, a new system called Thandeikta was proposed by
Nyaunggan Sayadaw, a Buddhist monk, in Year 1200 (1838 CE).
The new system was a hybrid between the original and the updated Surya schools. Unlike the new Surya, Thandeikta does not adopt the system of apparent reckoning; mean years and mean months are still used. It also retains the practice of placing the intercalary month always next to Waso and the intercalary day always at the end of Nayon, and only in a year which has an intercalary month. But Thandeikta follows the new Surya in small alterations of the length of the year and the month. The prevailing Metonic schedule was modified, and intercalary months were so fixed as to prevent further divergence between the solar and luni-solar years. With the support of Princess
Sekkya Dewi, who later became the chief queen of King Mindon, the new system was fully adopted in 1853. The first adjustment to then existing Metonic Cycle was made by putting an intercalary month in 1201 ME (1839 CE) instead of 1202 ME (1840).
While the new system has seemingly narrowed the gap between the calendar's solar and lunar years, it has not made the calendar more accurate when compared against the actual tropical year. Indeed, it is slightly worse than the old system. (The Thandeikta solar year is about 23 minutes 51.4304 seconds ahead of the mean solar year whereas Makaranta is about 23 minutes 50.8704 seconds ahead.) As a result, the calendar has kept on drifting away from the actual solar year. The calendarists have periodically resorted to modifying its intercalation schedule, based on apparent reckoning, to keep pace, at the expense of making publishing future calendars more than a few years out all but impossible.
In sum, at various times the calendar has used at least three slightly different methods of calculation to determine the insertion times of the intercalary day and month.
||Prior to 1215 ME (to 1853 CE)
||Metonic cycle determines intercalary day and month insertion points
||1215–1311 ME (1853–1950 CE)
||Modified Metonic cycle: # of excess days in the first 4 months determines intercalary day and month insertion points
||1312 ME (1950 CE) to present
||Current system used by Myanmar Calendar Advisory Board; Modified Metonic cycle: # of excess days in the first 8 months determines intercalary day and month insertion points
The calendar fell out of the official status in several mainland Southeast Asian kingdoms in the second half of the 19th century with the arrival of the European colonialism. The Gregorian calendar replaced the Burmese calendar in Cambodia in 1863, Burma in 1885 and Laos in 1889.[note 5] In 1889, the only remaining independent kingdom in Southeast Asia, Siam, also replaced the Burmese calendar and switched to the Gregorian calendar as the official civil calendar and Ratanakosin Era (with 1782 CE as Year 1) as the traditional lunisolar calendar.
Today, the calendar is used purely for cultural and religious festivals in Myanmar. Thailand has moved on to its own version of Buddhist calendar since 1941 although the Chulasakarat era dates remain the most commonly used and preferred form of entry by the academia for historical studies. The Chittagong Magi-San calendar, identical to the Arakanese calendar, is still used by certain ethnic minorities of Bangladesh.