Jérôme Lalande

Joseph Jérôme Lefrançois de Lalande was born in France on 11 July 1732. He turned his attention to the stars and joined the freemasons, but his lasting mark came in 1769 when he used observations of Venus crossing the face of the Sun to calculate a precise value for the astronomical unit — the Earth-to-Sun distance that anchors our sense of cosmic scale. The work required exacting measurement and gave astronomers a yardstick for the solar system. He continued writing and observing until his death on 4 April 1807.