Giovanni Domenico Cassini

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Giovanni Domenico Cassini
Meridian in the Basilica of San Petronio (Bologna), laid out in 1655 according to a design by Cassini

Giovanni Domenico Cassini (born June 8, 1625 in Perinaldo , County of Nice , Duchy of Savoy , † September 14, 1712 in Paris ) was an Italian astronomer and mathematician who gained fame in Bologna , was appointed to the Académie Royale des Sciences in Paris in 1669 , Took French citizenship in 1673 and has since been mostly called Jean-Dominique Cassini . He became the founder of a dynasty of astronomers to the French Revolution, the directors of the Paris Observatory presented, which is why he also Cassini I is called.

Life

Giovanni Cassini was born in Perinaldo ( Liguria ). He married the wealthy Geneviève de Laistre, became a French citizen in 1673 and began to write his first name Jean-Dominique . He went blind two years before his death. He died at the age of 87. He was buried in the Paris church of Saint-Jacques-du-Haut-Pas .

Act

Raccolta di varie scritture (1682)

Cassini studied at the Jesuit college in Genoa and Bologna . Under the influence of the former general and then Senator Cornelio Malvasia , he succeeded Father Bonaventura Cavalieri at the University of Bologna as professor of astronomy and mathematics in 1650 . There he taught Euclidean geometry and - according to the doctrine of the Catholic Church - Ptolemaic astronomy. He long preferred the geocentric model from Tycho Brahe , while hesitating to adopt the heliocentric model from Nicolaus Copernicus .

Cassini developed into a persistent, very precise observer of the sky. In 1655 he determined with his Meridiana in the Basilica of San Petronio in Bologna the inclination of the earth's orbit, the sun's diameter and the refraction of light in the earth's atmosphere. He quickly published his results in table form in 1662. In addition, the telescopes by Eustachio Divini (1610–1685) from Rome and Giuseppe Campani (1635–1715) made spectacular discoveries: with the help of the great red spot on Jupiter , Cassini determined its own rotation (1665). He also calculated the rotation times of Venus , Jupiter and Mars and examined the surfaces of the planets more closely. He derived the determination of longitude from the regular orbit of Jupiter's moon Io , an important step for geodesy and navigation. In addition, Cassini published exact tables in 1668 ( Ephemerides Bononienses mediceorum siderum ). After Jean Picard had spoken out in favor of him and achieved the goodwill of King Louis XIV , Cassini was appointed by Colbert in 1669 to the newly founded Académie Royale des Sciences and to head the Paris observatory , which was still under construction .

As director of the observatory, Cassini proved himself through far-sighted planning of expeditions with the aim of determining the exact shape of the earth, creating an accurate map of France and measuring the solar system. He discovered further Saturn moons (1671 Iapetus and 1672 Rhea ) and in 1675 for the first time the gap in Saturn's ring, which is now called the Cassinian division . Cassini noticed regular changes in brightness on Japetus. He realized that the moon always shows the same side to Saturn, that is, like the earth's moon rotates bound. He also described the zodiacal light in 1683 .

Cassini interpreted the 14 celestial bodies known at the time (6 planets and 8 moons) as the glorification of the Sun King Louis XIV. Today it is assumed that Cassini, out of admiration for his royal employer, had long kept quiet about the fact that he had discovered two other Saturn moons with Dione and Tethys . It was not until 1684 that he announced the discovery.

Cassini rejected the knowledge of Jean Richer and Philippe de La Hire about the flattening of the earth on the Poles, which had confirmed the predictions of Isaac Newton and Christiaan Huygens until 1683 . He imagined a flattening at the equator, just like his son and grandson later.

Between 1683 and 1718 the triangulation of the lengthening of his meridian arc Paris - Amiens to Dunkirk in the north and to Perpignan in the south, as proposed by Picard, was carried out by de la Hire , the Cassinis and the Maraldis , the results of which contradicted Cassini's view of a flattening at the equator.

In 1672 Richer determined the distance between Earth and Mars in Cayenne together with Cassini in Paris. From this, Cassini calculated a parallax of the sun of 9.5 ". This was the first time that the distance between the earth and the sun, today the astronomical unit , and thus all the distances in the solar system could be specified. However, the measurement accuracy was insufficient (the value was 7% too low), Cassini's result was not accepted by many, especially Edmund Halley .

In 1676 his colleague Ole Rømer formulated the hypothesis that the speed of light must be finite. Cassini initially agreed and then disagreed, because he was a supporter of the then prevailing assumption of instantaneous light propagation, which goes back to René Descartes .

His conservative attitude is also clear from the fact that he rejected Johannes Kepler's elliptical orbits and Newton's theory of gravity. Instead of ellipses, in 1680 he proposed a fourth-order curve, which is now called Cassini's ovals or Cassini's curve .

In 1693 he formulated three Cassini's laws for the orbit of the moon:

  1. The moon rotates evenly bound to its orbit.
  2. The lunar equator is constantly inclined by 1.5 degrees to the ecliptic .
  3. The axis of rotation of the moon always lies in the plane that is spanned by its orbital normal and the normal of the ecliptic (the slight deviation from this rule that can be observed is called physical libration ).

Jean-Baptiste Joseph Delambre in particular rightly branded Cassini as a traditionalist. Nevertheless, he is considered one of the most important astronomers in the 17th century. In 1672 he was elected a member of the Royal Society at the suggestion of Henry Oldenburg .

Cassini's successors as directors of the Paris observatory were his son Jacques Cassini (Cassini II), his grandson César François (Cassini III) and his great-grandson Jean Dominique (Cassini IV).

Honors

The Cassini orbiter and the asteroid (24101) Cassini were named after him, as well as the lunar crater Cassini after him and Jacques Cassini .

Fonts (selection)

See also

literature

  • Anna Cassini: Gio. Domenico Cassini. Uno scienziato del Seicento . Comune di Perinaldo, 1994 (Italian)
  • Michael Schütz: Cassini's Meridian in Bologna, Stars and Space , Volume 28, Number 6, 1989, pp. 362-366.
  • Rudolf Wolf: History of Astronomy . In: History of the Sciences in Germany. Modern times . At the instigation and with the support of His Majesty the King of Bavaria, Maximilian II. Ed. by the Historical Commission at the Königl. Academy of Sciences. tape 16 . Oldenbourg, Munich 1877, p. 449 ( Digitale-sammlungen.de ).
  • Jean Baptiste Joseph Delambre: Histoire de l'astronomie moderne . tape 2 . V e Courcier, Paris 1821, p. 686 ( full text in Google Book Search).
  • René Taton: Cassini, Gian Domenico (Jean-Dominique) (Cassini I) . In: Charles Coulston Gillispie (Ed.): Dictionary of Scientific Biography . tape 3 : Pierre Cabanis - Heinrich von Dechen . Charles Scribner's Sons, New York 1971, p. 100-104 .

Web links

Commons : Giovanni Domenico Cassini  - Collection of Images

Individual evidence

  1. ^ CC Gillispie (Ed.): Dictionary of Scientific Biography . I-XVIII, New York 1970-1990, Volume IV, p. 128.
  2. ↑ German: "Tables of the movements of the Jupiter satellites"
  3. ^ Jean Baptiste Joseph Delambre: Histoire de l'astronomie moderne . tape 2 . V e Courcier, Paris 1821, p. 598 ( full text in Google Book Search).
  4. ^ Rudolf Wolf: History of Astronomy . In: History of the Sciences in Germany. Modern times . At the instigation and with the support of His Majesty the King of Bavaria, Maximilian II. Ed. by the Historical Commission at the Königl. Academy of Sciences. tape 16 . Oldenbourg, Munich 1877, p. 615 ( Digitale-sammlungen.de ).
  5. ^ Entry on Cassini, Jean Dominique (1625 - 1712), Astronomer in the Archives of the Royal Society , London
personal data
SURNAME Cassini, Giovanni Domenico
ALTERNATIVE NAMES Cassini, Jean-Dominique; Cassini I
BRIEF DESCRIPTION French astronomer and mathematician
DATE OF BIRTH June 8, 1625
PLACE OF BIRTH Perinaldo , County of Nice , Duchy of Savoy
DATE OF DEATH September 14, 1712
Place of death Paris , France