Jean Richer

Jean Richer (* 1630, † 1696 in Paris) was a French astronomer. He was an employee of the astronomer Cassini I.

On behalf of the French government, he undertook from 1671 to 1673 a trip to Cayenne to determine Mars during its perigee. A comparison with observations in other locations enabled, on the basis of the parallax to determine the distance sun - Mars.

Richer certain exactly the length of a degree of a meridian arc, revealing the fact that the earth is flattened at the poles. He also stated that a second pendulum in Cayenne had to be shorter near the equator than in Paris, because Cayenne was farther away from the earth's center. Thus, hypotheses of Isaac Newton and Christiaan Huygens were confirmed. 1683 confirmed Philippe de La Hire by another expedition this fact.