THE ASTRONOMICAL ORIENTATION OF THE THAI PHRA THAT DOI SUTHEP TEMPLE IN RELATION TO THE ACRONYCHAL RISING OF ΑLPHA CORONA BOREALIS AND <italic>VISAKHA BUCHA</italic> DAY

: Astronomical orientation of ancient sites can reveal astronomical wisdom utilized to resonate with the context of the maker, thus providing additional insight into that ancient culture. In this study, the orientation of Phra That Doi Suthep Temple, a sacred Buddhist temple that was founded during the prosperous period of the ancient Lanna Kingdom (in Chiang Mai, in present-day Thailand), was investigated, as well as its connection to the tradition that many Buddhists walk up the mountain to the temple on the eve of Visakha Bucha Day ( Vesak Day—the Full Moon day of Vishākhā month). The remaining traces of historical evidence, including ethnic astronomical practices, suggest that the alignment of the temple when it was founded may have been related to the constellation now known as Corona Borealis (CrB), where α CrB is the reference star for the Vishākhā Nakṣhatra . To investigate this deduction, we surveyed the temple’s orientation using a theodolite and GPS, to obtain the azimuth of 59.74 ± 0.07° (30.26 ± 0.07° north of east). We employed Stellarium , which is precession-corrected, to determine the azimuth of α CrB and simulated that back in time to match that of the temple, thus yielding the estimated planning years. The finding suggests that the temple might be oriented to the true acronychal rising of α CrB in AD 1537 ± 19 in order to manifest the Full Moon on Visakha Bucha Day (a traditional Buddhist calendar’s New Year’s Day), close to the time when King Mueangketklao of Lanna reconstructed the temple on 21 April 1538.