Ce mois notre nouveau livre sera disponible; c'est la biographie d'un des astronomes français les plus importants du 19e siècle, François Félix Tisserand.
Born into a working-class family, his father was a cooper in the French wine making region of Nuits-Saint-Georges, Burgundy. He was an intellectual giant and his work on gravitational dynamics is on a par with that of his predecessor Pierre Laplace. He determined a method of how to identify the faint and nebulous comets and asteroids by their orbits. The 'Tisserand criterion' he defined continues to be used today as the only way of uniquely identifying such objects.
Tisserand est né dans une famille modeste à Nuits-Saint-Georges, une petite ville dans la région viticole de la Côte d’Or en Bourgogne. Son père était un tonnelier travailleur, mais Félix était un des géants intellectuels: son travail sur la dynamique gravitationelle est l'égale de celui de son prédécesseur Pierre Laplace. Tisserand a découvert comment identifier les comètes nebuleuses et les astéroïdes par leur orbites. Aujourd'hui nous continuons à employer le critère de Tisserand parce que c'est le seul moyen d'identifier ces objets.
Neither comets nor asteroids have any distinguishing marks when observed from Earth. This meant, and still does today, that it was not possible to definitively identify such objects and distinguish them from previous comets or asteroids observed.
(Image courtesy of NASA)
Comet 332P/Ikeya–Murakami, lower left in the picture above, showing typical comet characteristics of nebulosity. Asteroids, whilst not nebulous in image, are too small for any distinctive surface features to be seen.
Because of their elliptical orbits, and the location of the main asteroid belt between Mars and Jupiter, the orbits of comets and asteroids are subject to gravitational disturbance (‘perturbations’) by the gravitational ‘spheres of influence’ of the major planets and solar system objects.
This means that these objects are often not quite where their orbital predictions would place them. The challenge was to be sure that the object we were currently observing is either the same as an object previously seen, or to be able to conclusively recognise it as a newly discovered object.
Tisserand solved this problem by showing mathematically that a combination of orbital parameters (elements) always remained the same before, during and after any gravitational encounter. The Tisserand criterion is a unique value that is assigned to small solar system objects.
(Non-gravitational forces can also affect their orbits. More details on these, together with orbital descriptions on the various types of asteroid and a simplified derivation of the Tisserand criterion, are available in our book on the asteroids.)
Although best remembered for his work on celestial mechanics, Félix Tisserand was also a member of the Board of Longitude and Académie des Sciences, and director at Toulouse and Paris observatories.
He undertook three expeditions, to Japan, Malaysia and Martinique as part of his work in determining the scale of the solar system, and succeeded Urbain Le Verrier as the director of the Paris observatory after Le Verrier’s tumultuous governance of the institution.
Far from being a remote or unapproachable intellect, Félix Tisserand was also a 'people-person' and all those who came into contact with him remarked on his good nature, character and diligence.
During his tenure as the director of Toulouse Observatory he was visited by Charles Smyth, the 2nd astronomer royal for Scotland. Smyth’s diaries give a fascinating insight into the good natured, social but very diligent character of his host.
Remarkably, very few people today, including astronomers, will have heard of Tisserand or his achievements. He suffered more personal tragedies in his life than most, yet his modesty, his kind nature and his skills in communicating and teaching both mathematics and astronomy continued to shine through.
On a personal note, I have always been inspired by Tisserand and his work during my studies into gravitational dynamics. And we found researching his life within one of the best wine producing areas of France a delightful venture! I hope you enjoy reading our short biography on this great man as much as we have enjoyed uncovering the life and works of this forgotten, truly genius.
Anyone planning or considering a holiday in Burgundy should find Tisserand particularly interesting, and Nuits-Saint-Georges and the nearby city of Dijon offer a charming place for a holiday!
Referenced and topical web-pages
Major Planet Centre
Jet Propulsion Laboratory small-body database
The original source for the above image of Comet 332P/Ikeya–Murakami