Jérôme Lalande

Joseph Jérôme de Lalande Lefrançais ( born July 11, 1732 in Bourg -en- Bresse, France, † April 4, 1807 in Paris) was a French mathematician and astronomer during the period of the Enlightenment and the French Revolution. During the Revolution, he had the title of nobility "de" fall.

Life and work

Lalande attended a Jesuit school, and then began a law of science studies. After he gets to know the astronomer Joseph Nicolas Delisle in Paris, he studied astronomy at Delisle and theoretical physics with Pierre Lemonnier.

Despite a committed observer activity as Delisle's assistant, he graduated in 1751 - that is, with only 19 years - the study of law and practiced in his home from Bourg -en- Bresse. After stimulating contacts with Pierre- Louis Moreau de Maupertuis and Leonhard Euler in Berlin Lalande published some of his measurements reductions in the releases of the Academies of Berlin and Paris. His work led to the appointment as a Foreign Member of the Prussian Academy of Sciences and in 1752 director of the Berlin Observatory. In 1753 he was elected to the Académie des Sciences ( 1753). Then there was a dispute with his teacher Lemonnier on the correct calculation of the flattening of the earth, for the calculation of the lunar orbit ( Equatorial horizontal parallax ) was used. A commission of the Paris Academy ruled in favor of Lalande. For this, however, it was just a " Pyrrhic victory ", because his relationship with his teacher Lemonier then cooled.

Path calculation of Halley's comet

Lalande then worked as an assistant to Alexis -Claude Clairaut on a better path calculation of Halley's comet, leading to employment (as with Clairaut, d' Alembert and Euler ) led to the three-body problem. Using methods Clairauts Lalande was able to successfully calculate the perturbations of the comet by large planets. He was supported in the extensive computational work by Nicole -Reine Lepaute (1723-1788), whose contribution as the other former mathematicians, who were allowed to run for their male colleagues " raking ", was largely ignored. Lalande praised her work as:

For six months, we calculated from morning to night .. The help Mme Lépautes was such that the enormous amount of work I had ever can not tackle without it. It was necessary for each successive degree over 150 years to calculate the distance between the two planets Jupiter and Saturn to the comet separately away.

Later Lalande often cooperated with mathematicians. Lalande girlfriend Louise du Pierry ( born in 1746 ) was later first astronomy professor.

In " Halley " caused unusually strong perturbations by Jupiter, the comet would come months later near the Earth's orbit than expected. Charles Messier was looking for him in vain until 1757; he was spotted late 1758 by Johann Georg Palitzsch the first time and the perihelion in March 1759 agreed to four weeks - which was a great success for the new perturbative methods. Lalande prediction was regarded by contemporaries as a triumph of mainly mechanistic worldview of the Enlightenment.

Today it is known by other methods ( mainly due to the possible by computer numerical integration of small steps ) that Halley's orbital period is not only then modified by one year: their value, which is on average 76 years, fluctuated in the last 2000 years between 74 and 79 years.

Only 40 years after Lalande succeeded Heinrich Olbers to develop faster methods of path calculation of comets.

University teacher

After this success, Lalande 1762, succeeding his teacher Deslisle as professor of astronomy at the Collège Royale, which he remained until his death. 1760 to 1776 he was also editor of the Connaissance des temps, the most important astronomical yearbook in France. In 1791 he became rector of the College de France, and sat among other things, the admission of students through.

As an astronomer, he worked for example in the development of "lunar distances " to stars, which were then considered as a method to solve the very important for shipping navigation length problem.

Also at the processing of data of Venus passages 1761 and 1769, including James Cook in the South Seas performed ( Endeavour expedition, Charles Green led in June 1769 to the observations from Tahiti ), Lalande was involved. It succeeded Lalande 1771, submitted from global observations of Venus transits of 1761 and 1769 an improved calculation of the Earth's orbit. His statement that " astronomical unit " of 153 ± 1 million km is consistent with the current of 149.6 million kilometers already up to 2%. The same value was Johann Franz Encke in 1835, while pingre came to 142.9 million kilometers.

On November 24, 1763 Lalande was inducted into the Royal Society. In 1764 he published his textbook of astronomy, which was also a manual for measurements and their "reduction" and measuring instruments. The described therein calculation methods for comets in 1800 influenced the young businessman Friedrich Wilhelm Bessel to turn to astronomy. Lalande also wrote popular books such as his " Astronomy des Dames ".

1765 to 1766 he traveled to Italy, where he asked for an audience with the Pope, to take the works of Nicolaus Copernicus and Galileo from the "Index". 1769 appeared to be more extensive trip report from Italy. On another visit to England he also saw the famous clock in Greenwich Harrison, who eventually solved the length problem in an improved form.

As of 1783 his most gifted student Jean -Baptiste Joseph Delambre was his assistant, the Lalande 1788 (Letter to Bugge ) as designated " currently most astronomer worldwide." After Delambre had in 1789 received the Grand Prix of the Academy for his calculation of the orbit of Uranus, Lalande wrote him about his observatory.

In May 1795 Lalande was director of the Paris Observatory. There was a first star catalog with 30,000 stars in 1797 expanded to 41,000. His niece by marriage and illegitimate daughter, Marie -Jeanne de Lalande ( Amélie Harlay, 1768-1832 ) and his cousin Michel, husband of Marie -Jeanne, there were his employees.

The reconnaissance Lalande was a known atheist, what process is good for him during the French Revolution. In 1799 he published his Dictionary of Atheists, in which he recorded later for its unwillingness even Napoleon Bonaparte. Its " ugliness " was the goal of many contemporary cartoons. He himself took no offense and was thus not in his relationships with women bother.

His wit manifests itself for example in the following anecdote. It was generally known that Voltaire did not like cats. When Voltaire blasphemed, they would not have even made ​​it as animals to the 33 constellations named Lalande a constellation Felis ( cats), but this was removed a short time later from the sky maps. In contrast, the astronomers Congress decided in 1798 in Gotha (see Franz Xaver von Zach and Johann Elert Bode) that also suggested by Lalande " Aerostat " should remain.

Freemasons and encyclopedist

Jérôme Lalande is listed among the 72 names of prominent persons on the Eiffel Tower.

Claude Adrien Helvetius and his friend the Enlightenment in 1776 founded one of the most important Masonic lodges in the Age of Enlightenment, the so-called Philosophenloge Neuf Sœurs in Paris. He was her first Grand Master. For the Encyclopedia of Diderot and d' Alembert, he contributed 250 articles in the field of astronomy.

Writings

• Traité d' astronomy, 1764, another 4 volumes from 1771 to 1781, in 1792 appeared the third edition, edited by Delambre
• Abrégé de navigation historique, théorétique, et practique, (navigation charts) 1793
• Voyage d'un français en Italie, 1769 (8 volumes, trip report )
• Astronomy des dames 1785, new editions 1795, 1806
• Histoire Céleste Française, 1801 ( with an appendix with 47,000 cataloged stars ).