On this day, 289 years ago, on September 15, 1736 (August 11, 1736 in the lunar calendar), the French astronomer Bai was born. Bai (1736.9.15-1793.11.12) was a French astronomer known for calculating the orbit of Halley's Comet (1759) and studying the four known moons of Jupiter at the time. He was also a politician involved in the revolutionary activities of the time. Research on Halley's Comet began in 1759, and an observatory was built a year later to observe Jupiter's moons. In 1763, he was elected to the Academy of Sciences. His main works include "Essays on the Theory of Ganymede" published in 1766 and "On the Irregularities of Ganymede's Light Levels" published in 1771. The French Revolution interrupted his research. He was elected to the National Assembly as a delegate of Paris, was elected chairman of the Third Estate on May 5, 1789, and led the famous "Tennis Court Oath" on June 20. He served as the first mayor of Paris on July 15, 1789, and was re-elected mayor in August 1790, but his prestige was not as good as before, especially after he ordered the National Guard to disperse the rioting masses, which led to the Massacre of the Field of Mars on July 17, 1791. Bai retired on November 16, 1791. In July 1792, he went to Nantes, where he wrote the "Memoirs of Witnesses of the Revolution." In 1793, he was arrested while going to Meren to meet with his friend Laplace. On November 10, he was escorted to the Paris Revolutionary Court for trial and subsequently executed.