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1630 births1696 deaths17th-century French astronomers

Jean Richer

Adapted from Wikipedia · Discoverer experience

Historical print by Sébastien Leclerc showcasing an artistic scene from the past.

Jean Richer (1630–1696) was a French astronomer and assistant at the French Academy of Sciences, working under Giovanni Domenico Cassini. Between 1671 and 1673, he traveled to Cayenne in French Guiana to make important scientific observations.

Astronomical and gravimetric observations made on the island of Cayenne by Jean Richer, after an engraving by Sébastien Leclerc.

During his time in Cayenne, Richer observed the planet Mars when it was closest to Earth. This, along with observations made in Paris, helped scientists estimate the distance between Earth and Mars for the first time. He also measured the length of a seconds pendulum and discovered that gravity seemed to change depending on where you are on Earth.

His work helped scientists like Isaac Newton understand that Earth is not a perfect sphere, but bulges slightly at the equator. Though Richer returned to Paris in 1673, his findings were not published until 1679. After that, he worked on an engineering project in Germany, and little is known about the rest of his life. Most believe he passed away in Paris in 1696.

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