Pons, Jean-Louis (1761-1831)

Jean-Louis Pons was born in Peyre on 24. December 1761. His education was only basic, he was born into a poor family. During the first 28 years of his life there was no hint about Pons to be the most successful discoverer of comets.

In 1789 he got a post at the Observatory at Marseilles as concierge and got some instructions on astronomy by the observers. Pons learned fast and soon was allowed to do observations with the instruments. His favorite instrument was a telescope with a 3 degree wide field of view. He seems to have had an extraordinary ability to remember the star fields he observed and so to recognize changes to the observed area. He logged his first discovery of a comet on 11. July 1801 which he had to share with Messier who found it a day later. As it happened Pons' first discovery was also Messier's last. From this year on until 1827 Pons found a new comet almost every year.

His discovery of a comet in the early morning of 9. February 1808 was not confirmed until recently, when it was shown to be a passage of the periodic comet Grigg-Skjellerup which returns every 5 years

His work was rewarded in 1813 when he was promoted to assistant Astronomer and in 1818 assistant Director. For the three comets he discovered in that year he received the Lalande Prize, awarded by the Académie des Sciences in Paris. J. F. Encke followed a suggestion by Pons, who suspected one of the three comets to be the same one already discovered by him1  in 1805, and calculated the elements of the orbit. The comet was found to have a period of 3.3 years and Encke predicted its return for 1822. This return was only observable from the southern hemisphere and seen by K. Ruemker from Australia. This comet is known today as 'Encke's Comet', but Encke himself always referred to that one as 'Pons' Comet'.

The Astronomical Society in London awarded Ruemker and Pons with silver medals, Pons received his for the discovery of two new comets in 1822.

These comets were discovered by Pons from the observatory at Marlia near Lucca (Italy), where he had been director from 1819 on. He had been called to that post by the widow of the former King Louis of Etruria, Duchess Maria Luisa Bourbon-Parma, based on a recommendation by F.X. von Zach. In 1821 Pons had received another Lalande Prize, shared with J.N. Nicollet, for discovering more comets from his new observatory.

This observatory was closed when the Duchess Maria Luisa died in 1824. Pons was invited in 1825 by the Grand Duke of Tuscany, Leopold II., to become the director of the Florence Observatory. This was again with the recommendation of F.X. von Zach.

In Florence he discovered seven more comets, the last one in August 1827. In that year he was awarded another Lalande Prize, his third, shared with J.F.A. Gambart. 26 comets bear the name of Jean-Louis Pons, but he discovered or co-discovered up to 37.

From 1827 on Pons' eyesight faded and he had to stop observing completely in the first months of 1831.

Pons died in Florence on 14. October 1831. He is honored by a lunar crater named after him.

1 Chapin suggests that Encke had seen the comet in 1805. I doubt this, since Encke was only 14 years of age at that time.

1. CHAPIN, S.L., in: Dictionary of Scientific Biography, Vol. 11, p. 82-83.
2. LEVY, D.H., The Quest for Comets, 1994, p. 52-54
3. NEWCOMB & ENGELMANN, Populaere Astronomie, 1922 (7. Ed.), p. 818
4. AUDOUZE, J. & ISRAËL, G., Cambridge Atlas of Astronomy, 3. Ed., p. 110 5. Poggendorff, Vol. 1 (1863), p. 498
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