July 11: Joseph Lalande

Joseph Jérôme Lefrançois de Lalande

July 11, 1732 – April 4, 1807

Joseph Lalande was a French astronomer and writer.

Lalande was born at Bourg-en-Bresse. His parents sent him to Paris to study law, but as a result of lodging in the Hôtel Cluny, where 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 Lemonnier obtained permission to send him to Berlin, to make observations on the lunar parallax in concert with those of Lacaille at the Cape of Good Hope.

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 corrected edition of Edmond Halley's tables, with a history of Halley's Comet whose return in that year he had helped Alexis Clairaut 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 Delambre, Giuseppe Piazzi, Pierre Méchain, and his own nephew Michel 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.

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 and the Lalande prize instituted by him in 1802 for the chief astronomical performance of each year still testifies to his enthusiasm for his favourite pursuit.

His star catalog of 1801 contains many faint but nearby (and thereby low mass) stars, so that a star name such as Lalande 21185 is almost guaranteed to refer to such a star, rather than a bluer, brighter, more distant one.

In 1765, Lalande was elected a member of the Royal Swedish Academy of Sciences. The crater Lalande on the Moon is named in his honor.