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Jean Richer
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Jean Richer was a French astronomer and assistant at the French Academy of Sciences, under the direction of Giovanni Domenico Cassini.
Astronomical and gravimetric observations made on the island of Cayenne by Jean Richer, after an engraving by Sébastien Leclerc.
Astronomical and gravimetric observations made on the island of Cayenne by Jean Richer, after an engraving by Sébastien Leclerc.
Astronomical unit
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The astronomical unit is a unit of length defined as 149597870700 m. Historically, the astronomical unit was conceived as the average Earth-Sun distance, before its modern redefinition in 2012.
Jean Richer
…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…
Transits of Venus across the face of the Sun were, for a long time, the best method of measuring the astronomical unit, despite the difficulties (here
Transits of Venus across the face of the Sun were, for a long time, the best method of measuring the astronomical unit, despite the difficulties (here, the so-called "black drop effect") and the rarity of observations.