Possible Orientation of the Phanom Rung Temple to Spica on Solar Saka New Year’s Day

In this paper, we explore the off-east orientation of Prasat Hin Phanom Rung, a Khmer-style Hindu temple in northeastern Thailand that may have been aligned to a specific star in accordance with Vedic architectural rules known as Vastu Shastra. Our archaeoastronomical site survey yielded the temple’s axis, which we then compared to the azimuths of various stars during the Khmer Empire. Using Stellarium to calculate precession we found that Spica was the only star that coincided with the western gate of the temple. Carvings and inscriptions strengthen the case for intentional alignment to Spica and link the cosmical setting of the star to the first day of the new year according to the Saka calendar, in which it would be seen setting at dawn as the Sun began to cross the Vedic zodiac sign of Mesha Rasi (Aries). The dating analysis suggests the period for the planning and founding of the original temple to be 760–850 AD.