สำนักงานราชบัณฑิตยสภา

ปฏิ ทิ นจั นทรคติ : ... 48 The Journal of the Royal Institute of Thailand Vol. 39 No. 2 April-June 2014 be caused by errors in the Thai lunar calendar: an effect on the date of the Buddhist lent in each year, effect on the Buddhist memorial dates, effect on the Thai cultural dates, and an effect on identifying seasons in Thailand. These effects can be reduced or may not occur, if the Thai lunar calendar can identify date and time of the “full moon” on the reference meridian of Thailand correctly every lunar month. This identification is most important for those who involve in both the preparations and the uses of the lunar calendar in Thailand, in expecting it to be accurate. In addition, the paper aims to present an astronomical calendar called “Thai astronomical lunar calendar” that in- dicates phase and position of the Moon together with an angular distance of the Moon from the reference stars (the astrological auspices) in the ecliptic coordinate system. This astronomical calendar may be a source of information used to improve the Thai lunar calendar because it helps to define the appropriate formulation of an astronomi - cal terminology; “the date of the full moon” or “the 15 th date of the waxing moon”. Moreover, it can be a data used for better specifying “the leap month” and “the leap day” of the Thai lunar calendar. If the Thai lunar calendar can specify “the 15 th date of the waxing moon in the 8 th Thai lunar month” and “the 15 th date of the waxing moon in the second 8 th Thai lunar month”, it follows that the date of the Buddhist lent will be after the true full moon appearing close to the “Pubbasatha auspice (Delta-Sagitttarii)” and “Uttarasatha auspice (Sigma-Sagitttarii)” respectively. This corresponds to the rainy season in Thailand and the Thai lunar calendar will be accepted from all related sectors in the country. Keywords: solar calendar, lunar calendar, Moon, phase of theMoon, full moon, the full moon date, the 15 th date of the waxing moon, the Buddhist lent