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Jerome Lalande had calculated the return of Halley’s comet & observed Neptune in 1795


Nov 28, 2016
 
Lalande
 
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During the 18th century, some people’s minds were already traveling to space.

One such man, Jerome Lalande, had almost discovered Neptune, was devoted to planetary theory and corrected Alexis Clairaut’s calculations about the return of Halley’s comet.

Jérôme LalandeJérôme Lalande

Lalande was born at Bourg-en-Bresse and didn’t have any brothers or sisters. His parents wanted him to study law so they sent him to Paris.

But coincidentally, or maybe guided by the laws of the Universe, the law student took a room in the Hotel Cluny.

In the same hotel, the astronomer Joseph-Nicolas Delisle had an observatory by which Lalande was enchanted and soon became overwhelmed by astronomy.

He had an excellent understanding of it and became the favorite pupil of Delisle and Charles Le Monnier who persuaded him to devote to astronomy.

Joseph-Nicolas DelisleJoseph-Nicolas Delisle

Lalande completed his law studies and was supposed to return home to obtain a practice as an advocate.

At the same time, Lemonnier offered him his place in Berlin where he could make observations on the lunar parallax in concert with those of the 1750 expedition to the Cape of Good Hope, led by Nicolas Louis de La Caille.

Lalande was only 21 years old when he left to Berlin. His work had proven to be so successful that it earned him an admission to the Academy of Berlin and he was soon elected as an adjunct astronomer of the French Academy of Sciences.

Quarter of a circle by Jonathan Sisson used by Jérôme de Lalande to measure the distance between the earth and the moon in 1751. Photo creditA quarter of a circle by Jonathan Sisson used by Jérôme de Lalande to measure the distance between the earth and the moon in 1751. Photo credit

While Alexis Clairaut was working on precise calculations regarding the return of the Halley’s comet in 1682,  predicted by Halley to return in late 1758 or early 1759, Lalande was the one who contributed to Clairaut’s work, providing the final and correct result. The Halley comet returned just as Lalande calculated. Clairaut became popular and was acclaimed in the press as a great vindication of Newton’s law of gravitation.

Lalande was still admired by many astronomers, mostly by Delisle who in 1762 resigned the chair of astronomy in the Collège de France in Lalande’s favor. Lalande had actively published astronomical textbooks and in 1769, became a famous practical astronomer with the publication of his work on the transit of Venus. He also wrote about practical arts or published travel literature.

Lalande's "Astronomy" - Interior Cover, 1764Lalande’s “Astronomy” – Interior Cover, 1764

He loved seeing his name printed in the public press and once had said: “I am an oilskin for insults and a sponge for praise”. However, he was also known for his problematical personality which might had been the reason why he never had many friends or got married.

Statue of Lalande. Photo creditStatue of Lalande. Photo credit

In 1801, he created the Lalande Prize which was administered by the French Academy of Sciences and given to those who significantly contributed to the field of astronomy.

The first one awarded with this prize was the astronomer and Lalande’s disciple, Pierre-Antoine Véron, who determined the size of the Pacific Ocean from east to west.

Lalande's tomb at Pere-Lachaise cemetery. Photo creditLalande’s tomb at Pere-Lachaise cemetery. Photo credit

Lalande died in 1807 at the age of 74. Forty years after his death, the American astronomer Sears C. Walker was doing a historical research about possible pre-discovery of Neptune, which was discovered in 1846, and found out that Lalande did observations in the direction of Neptun in 1795.

Sears Cook WalkerSears Cook Walker

In Lalande’s records is written that “a star” had been observed but its position couldn’t be precisely determined. After the review of his papers, it was concluded that the star that Lalande had observed was the planet Neptune.

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The reason he couldn’t note its certain position was determined by the planet’s motion across the sky. The discovery of these records, concerning Neptune’s position in 1795, led to a better calculation of the planet’s orbit.

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