She worked on the predictions for the return of Halley's Comet in 1759. Such work required prodigious amount of computation, especially to determine the gravitational effect of Jupiter and Saturn on the Comet's orbit. She did other calculations for an annular eclipse of the Sun that would be visible in France. She produce a chart showing the time and percentage of the eclipse for all of Europe. This work was done to aid the French Astronomer Joseph Lalande.
She also assisted her husband, who was the royal clockmaker of France. She produced the table of the number of oscillations per unit time of pendulums of various lengths for the book that was published under her husband's name, Traite d'horlogerie. The beautiful rose Hortensia is named for her.
These tables and catalogs were crucial for the development of modern astronomy. Each one contributed its part to a growing body of work that culminated in such great catalogs as the guide star catalog that steered the Hubble Space Telescope. Almost every satellite carries aboard a star catalog to orient its way around the sky.
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