สำนักงานราชบัณฑิตยสภา

วารสารราชบัณฑิตยสภา ปีที่ ๔๑ ฉบับที่ ๓ ก.ค.-ก.ย. ๒๕๕๙ 83 ลอย ชุนพงษ์ทอง Abstract Adhikamas Calculation in Dynamic System Loy Chunpongtong Adviser to the Royal Thai Calendar Calculation, Bureau of the Royal Household The Thai Royal Calendar is a lunisolar calendar with very restrictive rules. Complexity arises because the synodic month and the sidereal year cycles of revolution do not comprise an integral number of days nor are they perfectly commensurable with each other. In addition, the synodic month cycle is not a constant number. The objective of this research is to define mathematic functions requiring a complex sequence of 12 (regular, ปกติมาส) and 13 (intercalary, อธิกมาส) months per year. The research focuses on determining intercalary year and has created a new method of determining such years in the Royal Thai calendar. It is the first mathematical method that incorporates modern dynamic astronomical models to minimize the variances of traditional calendars and corresponds to the historical records perfectly. Keywords: Royal Thai calendar, determining intercalary, dynamic model