section_path: Structure/Year/Types of calendar year
section_name: Types of calendar year
paragraph_text: Types of calendar year
  
  The Burmese calendar is a lunisolar calendar in which the months are based on lunar months and years are based on solar years. One of its primary objectives is to regulate the lunar part that it will keep pace with the solar part. The lunar months, normally twelve of them, consist alternately of 29 days and 30 days, such that a normal lunar year will contain 354 days, as opposed to the solar year of ~365.25 days. Therefore, some form of addition to the lunar year (of intercalation) is necessary. The overall basis for it is provided by cycles of 57 years. Eleven extra days are inserted in every 57 years, and seven extra months of 30 days are inserted in every 19 years (21 months in 57 years). This provides 20819 complete days to both calendars.
  
  As such, the calendar adds an intercalary month (ဝါထပ်) in leap years (ဝါငယ်ထပ်နှစ်) and sometimes also an intercalary day (ရက်ငင်) in great leap years (ဝါကြီးထပ်နှစ်). The intercalary month not only corrects the length of the year but also corrects the accumulating error of the month to extent of half a day. The average length of the month is further corrected by adding a day to Nayon at irregular intervals—a little more than seven times in two cycles (39 years). The intercalary day is never inserted except in a year which has an intercalary month. The Hindu calendar inserts an intercalary month at any time of year as soon as the accumulated fractions amount to one month. The Burmese calendar however always inserts the intercalary month at the same time of the year, after the summer solstice while the Arakanese calendar inserts it after the vernal equinox.
  
  The actual calendar year (Wawharamatha Hnit, ဝေါဟာရမာသနှစ်) consists of 354, 384 or 385 days.
  
  The Thai Chulasakarat calendar uses a slightly different method to place the intercalary day. Instead of it in a leap year as in the Burmese system, the Thai system places it in a separate year. Thus, the Thai small leap year has 355 days while the Thai great leap year has 384 days. Both systems arrive at the same number of days in a 19-year cycle however. Furthermore, in contrast to Indian calendars, the Burmese calendar follows a Metonic cycle in which intercalary months are inserted on a set schedule. However, because the Burmese calendar has to adjust for the use of Indian-calendar-derived sidereal years with the Metonic cycle's tropical years, maintaining a set Metonic cycle has been a challenge.
  
  The calendar seems to have employed several schedules to determine which of the 19 years will be intercalary years. To find out which year will have an intercalary month, divide the Burmese year by 19. The quotient is the expired cycles. If the remainder tallies with the set sequence number of the prevailing Metonic cycle, then it will be an intercalary year.