From Live Science: Solar Eclipses and Thailand’s Kings – A Curious History
For King Narai, who enjoyed diplomatic ties with the “Sun King,” Louis XIV of France, the “new astronomy” taught by French Jesuit missionaries had important uses for time-keeping and map-making. (Louis XIV himself, after ordering France to be accurately measured with the latest astronomical techniques, grumbled that his astronomers had lost more of his territory than his generals.)
After hearing from visiting French missionaries about the Observatory at Beijing, which had been refitted by Jesuit astronomers for the emperor of China, Narai ordered an observatory built on the grounds of his palace at Lopburi (the ruins of which can be seen today) … It was equipped with the latest European technology, and in 1685, under the guidance of French astronomers, King Narai watched through a telescope an eclipse of the moon.
King Narai of Ayatthuya and his court with French Jesuit astronomers and missionaries observing an eclipse of the moon in 1685
On April 30, 1688, King Narai had his first chance to observe an eclipse of the sun at Lopburi, but it would also be his last. A Thai court painting … shows a Thai nobleman named Phetracha watching the eclipse projected on a screen while crouched on his elbows and knees in the style of the court. Phetracha resented the king’s friendships with foreigners, and may have feared that the king might convert to Christianity …
30 April 1688: King Narai with French astronomers and missionaries among the court at the observatory in Lopburi, now in central Thailand, for the obervation of a partial solar eclipse
According to legend, a fortune teller had warned Phetracha to watch for a sign from heaven that he would become king, and it seems he took the eclipse as a premonition of his ascension: Just days later, he deposed Narai, crowned himself king, and either executed or ordered foreigners out of the kingdom.
August 1868: King Mongkut of Siam with foreign members of his expedition to Wa Ko, now in southern Thailand, for the obervation of a total eclipse of the sun
For the solar eclipse on Aug. 18, 1868, King Mongkut invited foreign astronomers and important guests to the village of Wa Ko, near the southern port of Prachuap Khiri Khan, which his astronomical calculations had determined would be the best site for scientific observations of the event. Steamships ferried workers and supplies from the capital to build an observatory and residences for hundreds of guests and dignitaries, including almost the entire Thai court, senior French and British diplomats, and a French-led astronomical team.
Foreign astronomers and guests with telescopes at the observatory built for King Mongkut’s 1868 expedition to Wa Ko to observe the solar eclipse
Mongkut’s predications of the exact timing of the eclipse would be proof of his efforts to reform the Siamese calendar and astronomy — and his rebuke to his court astronomers. According to a report from a French diplomat who was present, the king proudly reported that the French astronomers had confirmed that his predictions were of greater accuracy than their own, says historian Thongchai Winichakul in his book “Siam Mapped”. But for King Mongkut, as for King Narai, this first solar eclipse would also be his last; like many who journeyed to Wa Ko, Mongkut caught malaria and died in Bangkok a few weeks later.
Sketches of the solar eclipse of 18 August 1868 at Wa Ko by French astronomer Edouard Stephan
Read more at Live Science: Solar Eclipses and Thailand’s Kings – A Curious History