Jean Richer

Jean Richer

Jean Richer (1630–1696) was a French astronomer and assistant (élève astronome) at the French Academy of Sciences, under the direction of Giovanni Domenico Cassini. Between 1671 and 1673 he performed experiments and carried out celestial observations in Cayenne, French Guiana, at the request of the French Academy. His observations and measurements of Mars during its perihelic opposition, coupled with those made simultaneously in Paris by Cassini, led to the earliest data-based estimate of the distance between Earth and Mars, which they then used to calculate the distance between the Sun and Earth (the astronomical unit). While there he also measured the length of a seconds pendulum, that is a pendulum with a half-swing of one second, and found it to be 1.25 lignes (2.256 millimeters) shorter than at Paris. Read more on Wikipedia

His biography is available in different languages on Wikipedia. Jean Richer is the 424th most popular astronomer (down from 363rd in 2019). (down from 3,389th in 2019)