Lalande was born at
Bourg-en-Bresse (
département of
Ain) to Pierre Lefrançois and Marie‐Anne‐Gabrielle Monchinet. His parents sent him to Paris to study law, but as a result of lodging in the Hôtel Cluny, where
Joseph-Nicolas Delisle had his observatory, he was drawn to astronomy, and became the zealous and favoured pupil of both Delisle and
Pierre Charles Le Monnier. Having completed his legal studies, he was about to return to Bourg to practise as an advocate, when Le Monnier obtained permission to send him to
Berlin, to make observations on the lunar
parallax in concert with those of
Nicolas Louis de Lacaille at the
Cape of Good Hope. , used by
Jérôme Lalande to measure the distance between the Earth and the Moon in 1751. The successful execution of this task obtained for him, before he was twenty-one, admission to the
Academy of Berlin, as well as his election as an adjunct astronomer to the
French Academy of Sciences. He now devoted himself to the improvement of the planetary theory, publishing in 1759 a corrected edition of
Edmond Halley's tables, with a history of
Halley's Comet whose return in that year he had helped
Alexis Clairaut and
Nicole-Reine Lepaute to calculate. In 1762, Delisle resigned the chair of astronomy in the Collège de France in Lalande's favour. The duties were discharged by Lalande for forty-six years. His house became an astronomical seminary, and amongst his pupils were
Jean Baptiste Joseph Delambre,
Giuseppe Piazzi,
Pierre Méchain, and his own nephew
Michel Lefrançois de Lalande. By his publications in connection with the
transit of Venus of 1769 he won great fame. However, his difficult personality lost him some popularity. In 1766, Lalande, with
Claude Adrien Helvétius, founded the
Les Sciences lodge in Paris, and received its recognition from
Grand Orient de France in 1772. In 1776, he changed its name to
Les Neuf Soeurs, and arranged for
Benjamin Franklin to be chosen as the first worshipful master. Although his investigations were conducted with diligence rather than genius, Lalande's career was an eminent one. As a lecturer and writer he helped popularise astronomy. His planetary tables, into which he introduced corrections for mutual perturbations, were the best available up to the end of the 18th century. In 1801, he endowed the
Lalande Prize, administered by the
French Academy of Sciences, for advances in astronomy.
Pierre-Antoine Véron, the young astronomer who for the first time in history determined the size of the Pacific Ocean from east to west, was Lalande's disciple. Lalande was an atheist, and wrote a dictionary of atheists with supplements that appeared in print posthumously. He never married. He was believed to have an illegitimate daughter
Marie-Jeanne de Lalande whom he trained in mathematics so that she could help him with his work; according to more recent research she was not his daughter. ==Near discovery of Neptune==