Jean Sylvain Bailly (French pronunciation: ​[ʒɑ̃ silvɛ̃ baji]; 15 September 1736 – 12 November 1793) was a French astronomer, mathematician, freemason, and political leader of the early part of the French Revolution. He presided over the Tennis Court Oath, served as the mayor of Paris from 1789 to 1791, and was ultimately guillotined during the Reign of Terror.