สำนักงานราชบัณฑิตยสภา

47 นิ พนธ์ ทรายเพชร วารสารราชบัณฑิตยสถาน ปีที่ ๓๙ ฉบับที่ ๒ เม.ย.-มิ.ย. ๒๕๕๗ อารี สวัสดี และ วรพล ไม้สน, “ดาราศาสตร์ราชส� ำนัก” สถาบันวิจัยดาราศาสตร์แห่งชาติ (องค์การมหาชน), พ.ศ. ๒๕๕๖. Peter Duffett-Smith, Practical Astronomy with your Calculator 3 rd edition, Cambridge University Press, 1988. Abstract Lunar Calendar: Effects that May Be Caused by Errors in the Thai Lunar Calendar and a Development of Lunar Data Using Astronomy Knowledge Nibondh Saibejra Fellow of the Academy of Science, The Royal Institute, Thailand Jaturong Sukonthachat Academic committee in the preparation of the dictionary of astronomy, Academy of Science, The Royal Institute Department of Physics, Faculty of Science, Srinakharinwirot University This article discusses the lunisolar Buddhist calendar used widely in Thailand, which includes the data of the Gregorian calendar and the Thai lunar calendar, a calendar indicating the day-month-year according to the Moon’s phase and its position in the sky. There are 3 ways to calculate lunar data used in the Thai lunar calendar: calculating an average phase and an approximate location of the Moon as in the scripture named Suriyayart, finding an average phase of the Moon using an iteration on the Thai special board named Pakkhaganana, and calculating the true phase and the true position of the Moon using astronomy knowledge. In order to find the average lunar data in the first 2 approaches, they are calculated using a hypothetical lunar orbit at a constant speed with an approximate average period of 29.530583215 and 29.530593514 days respectively. The 3 rd approach is to determine the true lunar phase by using the true Moon orbit at an inconsistent rate with the average period of 29.530587981 days. Because the Thai lunar calendar uses data obtained from the Suriyayart, causing Buddhist sabbath (the 8 th , the 15 th , the 23 rd and the 29 th or 30 th day of the Thai lunar months) to be faster than it should be according to the true Moon’s phase by about 1 day up to 24 and 34 times in the Buddhist year 2556 and 2557 respectively. The article proposes 4 effects that may