National Science Day is observed in

National Science Day is observed in Thailand every year on August 18. This holiday celebrates the anniversary a total solar eclipse in 1868, that was predicted by King Mongkut two years earlier.
King Mongkut (Rama IV) is one of the most revered monarchs of Thailand. Before he assumed the throne of the king, he had been a monk. During the monkhood he studied astrology, astronomy and mathematics. These developed his skills in astronomical measurement, that helped him to change official Buddhist calendar, that was miscalculated, that is why times for auspicious moments were incorrect. His another achievement was prediction of the Solar eclipse, that would occur on August 18, 1868.

In 1982 King Mongkut was proclaimed to be the Father of the science in Thailand. There was another proclamation, that concerned annual celebration of National Science Day on August 18. Since then this holiday has become one of the most revered days in the Thai calendar of the public holidays.