Burmese calendar

The Burmese calendar or Myanmar Era ) 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, Xishuangbanna, 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. 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 recalibrated the calendar, naming the new era Kawza Thekkarit 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 may also have been in use in the Pyu states. Mainstream scholarship, however, holds that the recalibrated calendar was launched at Sri Ksetra, and later adopted by the upstart principality of Pagan.

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. 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 submitted to King Anawrahta and adopted the calendar in the mid-11th century in place of Mahāsakaraj, the standard calendar of the Khmer Empire. 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 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. One key difference from Indian systems was that the Burmese system followed a 19-year intercalation schedule. It is unclear from where, when or how the Metonic system was introduced; hypotheses range from China to Europe.
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.
The earliest attempts on record to change the calendar were superficial. On the 800th anniversary of the calendar, King Mohnyin Thado recalibrated the calendar to Year 2. 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 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 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 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.
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 instead of 1202 ME.
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. 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.

Era	Definition	Description
Thuriya Theiddanta	Prior to 1215 ME	Metonic cycle determines intercalary day and month insertion points
Thandeikta	1215–1311 ME	Modified Metonic cycle: # of excess days in the first 4 months determines intercalary day and month insertion points
Current	1312 ME 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 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. 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 as the traditional lunisolar calendar.
In Burma, 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.
The Chittagong Magi-San calendar, identical to the Arakanese calendar, is still used by Chakma and Marma ethnic minorities of Bangladesh.
Today, the Calendar Advisory Board within the Ministry of Religious Affairs and Culture of Myanmar is tasked with keeping the lunisolar calendar in line with the solar year.

Structure

Day

The calendar recognises two types of day: astronomical and civil. The mean Burmese astronomical day is from midnight to midnight, and represents 1/30 of a synodic month or 23 hours, 37 minutes and 28.08 seconds. The civil day comprises two halves, the first half beginning at sunrise and the second half at sunset. In practice, four points of the astronomical and civil day were used as reference points. The civil day is divided into 8 baho or 60 nayi , each baho equalling 7.5 nayi. In the past, a gong was struck every nayi while a drum and a large bell were struck to mark every baho.

Type	Time	Burmese name	Description
Day	1 o'clock	နံနက် တစ်ချက်တီး	midway between sunrise and midday
Day	2 o'clock	နေ့ နှစ်ချက်တီး	noon
Day	3 o'clock	နေ့ သုံးချက်တီး	midway between noon and sunset
Day	4 o'clock	နေ့ လေးချက်တီး	sunset
Night	1 o'clock	ည တစ်ချက်တီး	midway between sunset and midnight
Night	2 o'clock	ည နှစ်ချက်တီး	midnight
Night	3 o'clock	ည သုံးချက်တီး	midway between midnight and sunrise
Night	4 o'clock	နံနက် လေးချက်တီး	sunrise

Although the popular usage never extended beyond baho and nayi measurements, the calendar consists of time units down to the millisecond level.

Unit	Sub-units	Approximate equivalent time
yet ရက်	8 baho	1 day
baho ဗဟို	7.5 nayi	3 hours
nayi နာရီ	4 pat	24 minutes
pat ပါဒ်	15 bizana	6 minutes
bizana ဗီဇနာ	6 pyan	24 seconds
pyan ပြန်	10 khaya	4 seconds
khaya ခရာ	12 khana	0.4 second
khana ခဏ	4 laya	0.03333 second
laya လယ	1.25 anukhaya	0.00833 second
anukhaya အနုခရာ		0.00667 second

Only the following are used in calendrical calculations:

Unit	Sub-units	Approximate equivalent time
yet	60 nayi	1 day
nayi	60 bizana	24 minutes
bizana	60 khaya	24 seconds
khaya	60 anukhaya	0.4 second
anukhaya		0.00667 second

Therefore, modern time units can be expressed as:

Unit	Approximate equivalent Burmese units
hour	2.5 nayi
minute	2.5 bizana
second	2.5 khaya