Michel Lefrançois de Lalande

Michel Lefrançois de Lalande (21 April 1766 – 8 April 1839) was a French astronomer. He was the nephew and one of the main collaborators of astronomer Jérôme Lalande.

Biography Michel Lefrançois was born in Courcy, Calvados in 1766, the son of Jeanne Jourdan and Jean Lefrançois, first cousin of astronomer Jérôme Lalande. He took the name of his cousin Brother Jérôme, by order of the Court of the Seine on 13 June 1837 and became Le François de Lalande him and his descendants.

Jérôme de Lalande took Michel to Paris after the holidays of 1780 and immediately initiated him into his favorite study, that is, telescopic observation techniques, despite having the satisfaction of seeing him take an interest in them.

In 1792 he accompanied Jean-Baptiste Joseph Delambre, who was appointed to calculate the meridian arc of Dunkirk-Barcelona and thus the length of the meter. Then the Paris meridian and both begin to be measured around Paris..

Between 8 and 9 May 1795, at the age of 29, he detected a faint star which he took to be a simple star. Between the two observations, thanks to the large quarter-circle telescope of the École militaire, he noticed a gap and attributed it to his mistake. But he did not make a 3ª observation that would have allowed him to confirm the star's displacement from the first two observations and realize that it was an unknown planet, the planet Neptune, which was discovered 50 years later by Urbain Le Verrier.

In 1795 he was elected a member of the Bureau des Longitudes and, six years later, became a first-class resident member of the astronomy section of the French Academy of Sciences. He was also promoted to officer of the Legion of Honor. His grave is in the Père Lachaise, east cemetery.