Father Antoine Thomas and the Birth of ‘Modern Astronomy’ in Thailand

‘Modern astronomy’ was introduced to Siam (present-day Thailand) when the Belgian Jesuit missionary-astronomer Father Antoine Thomas carried out astronomical observations in 1681 and 1682 in order to determine the latitude and longitude of Ayutthaya. Three years later a contingent of French Jesuit missionary astronomers observed a total lunar eclipse from Lop Buri, which marked the start of an intensive two-and-a-half year period of observational activity at Lop Buri under the sponsorship of King Narai. This ended only with King Narai’s premature death in July 1688, and Western missionary-astronomers were then expelled from Siam.This situation only changed markedly nearly two hundred years later when another Royal supporter of astronomy, King Rama IV, invited French astronomers to observe the total solar eclipse of 18 August 1868 from Siam, and his son, King Rama V, hosted British astronomers during the 6 April 1875 total solar eclipse. Thailand’s romance with solar astronomy continued during the 9 May 1929 solar eclipse when King Rama VII visited British and German astronomers based near Siam’s southern border, and in the 1930s Thailand’s first astronomy course was taught at Chulalongkorn University.This chapter provides biographical information about Antoine Thomas, before examining the astronomical observations that he made in 1681 and 1682, and recent attempts to pinpoint his observing site. It then briefly sketches the development of ‘modern astronomy’ in Siam during the remainder of the seventeenth century, and in the nineteenth century, leading up to the emergence of professional astronomy during the twentieth century, and the formation of the National Astronomical Research Institute of Thailand in 2009