The Burmese calendar (, , or , ; Burmese Era (BE) or Myanmar Era (ME)) is a lunisolar calendar in which the months are based on lunar months and years are based on sidereal years. The calendar is largely based on an older version of the Hindu calendar, though unlike the Indian systems, it employs a version of the Metonic cycle. The calendar therefore has to reconcile the sidereal years of the Hindu calendar with the Metonic cycle's near tropical years by adding intercalary months and days at irregular intervals.
The calendar has been used continuously in various Burmese states since its purported launch in 640 CE in the Sri Ksetra Kingdom, also called the Pyu era. It was also used as the official calendar in other mainland Southeast Asian kingdoms of Rakhine, Lan Na, Chiang Hung, Lan Xang, Siam, and Cambodia down to the late 19th century.
Today, the calendar is used in Myanmar as one of the two official calendars alongside the Gregorian calendar. It is still used to mark traditional holidays such as the Burmese New Year, and other traditional festivals, many of which are Burmese Buddhist in nature.
History
Origin 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 (), 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.Irwin 1909: 2 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.Htin Aung 1970: 8–9
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 ( )Hmannan Vol. 1 2003: 216 with a Year Zero starting date of 22 March 638 CE.Eade 1989: 39 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.(Aung-Thwin 2005: 334–335): More research needs to be done. A Pyu stone inscription discovered in 1993 indicates that the Pyu states may have also used the Gupta Era. Mainstream scholarship, however, holds that the recalibrated calendar was launched at Sri Ksetra, and later adopted by the upstart principality of Pagan.Hall 1960: 8Aung-Thwin 2005: 35
Spread 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.Htin Aung 1959: 38–39 According to the Chiang Mai Chronicles and the Chiang 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.Oriental 1900: 375–376(Oriental 1900: 375–376): "The invasion of Lavo [Laos] ascribed to Anawrahta was more probably the work of some of his successors." However, scholarship says the earliest evidence of Burmese calendar in modern Thailand dates only to the mid-13th century.Eade 1989: 11
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.Smith 1966: 11Htin Aung 1967: 127 The Siamese adoption turned out to be the main catalyst for the calendar's usage in Cambodia,Eade 1989: 9 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 ( , which is believed to be chiefly based on the "original" Surya Siddhanta system of ancient India (i.e. Ardharatrika school).Ohashi 2007: 354–355 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.(Ohashi 2001: 398–399): Astronomers of ancient India certainly knew of the Metonic cycle, and may have introduced the concept to Southeast Asia. However, the Metonic cycle, is incompatible with sidereal based Hindu calendars, and thus was not (and still is not) used in Hindu calendars. (Chatterjee 1998: 151) suggests that the Metonic system was introduced to Burma by Europeans. (Ohashi 2001: 398–399) rejects Chatterjee's hypothesis saying that "no other trace of European influence is found in South-East Asian astronomy." Instead, (Ohashi 2001: 401–403) suggests that China may have been the source of the Metonic cycle.
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.Ohashi 2001: 398–399 Furthermore, the Burmese system did not incorporate advances in Indian calculation methods of the sidereal year until the mid-19th century.A.M.B. Irwin (Irwin 1909: 2–3) suggests that by 1738, the calendar was on the Makaranta system, an adaptation of the original Surya system. But J.C. Eade (Eade 1996: 17) doubts Irwin's assessment, saying he has found no differences with the original system still prevalent in mainland Southeast Asia at least to Pagan period inscriptions. Since the Burmese calendar was officially adopted only in 1564 in Siam, and since later Siamese calendars still used the original Surya, the Burmese calendar must have followed the original Surya at least to the 16th century, if not later. Even if the Makaranta system had come to be used in Burma in the following centuries, Ohashi (Ohashi 2007: 354–355) says the Burmese Makaranta system is "probably different from the well-known Indian Sanskrit astronomical table (Makarandasarani (1478 CE) of Makaranda, which follows the Saura school". (The original Thuriya Theiddanta system is 0.56 second a year slower (and more accurate) than later Indian systems.Irwin 1909: 7)
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).Eade 1995: 17 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.Rong 1986: 70 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.Irwin 1909: 2–3 Finally, a new system called Thandeikta was proposed by Nyaunggan Sayadaw, a Buddhist monk, in Year 1200 (1838 CE).Clancy 1906: 58
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.)Irwin 1909: 26–27 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.
EraDefinitionDescription Thuriya Theiddanta Prior to 1215 ME (to 1853 CE) Metonic cycle determines intercalary day and month insertion points Thandeikta 1215–1311 ME (1853–1950 CE) Modified Metonic cycle: # of excess days in the first 4 months determines intercalary day and month insertion points Current 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
Current status The calendar fell out of official status in several mainland Southeast Asian kingdoms (except Burma) in the second half of the 19th century with the arrival of European colonialism. The Gregorian calendar replaced the Burmese calendar in Cambodia in 1863 and Laos in 1889.(Simms and Simms 2001: 204–210) Laos became a French protectorate in March 1889, although the former overlord Siam would not acknowledge it until October 1893. 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 the Ratanakosin Era (with 1782 CE as Year 1) as the traditional lunisolar calendar.
In Burma (Myanmar), the Burmese calendar has not been replaced, but used alongside the Gregorian calendar after the fall of the Burmese kingdom. Thailand has moved on to its own version of the Buddhist calendar since 1941, although the Chulasakarat-era dates remain the most commonly used and preferred form of entry in academic use for historical studies.