Giovanni Domenico Cassini
Giovanni Domenico Cassini ( born June 8, 1625 Perinaldo near Nice, Italy, † September 14, 1712 in Paris), from 1673 also called Jean -Dominique Cassini I., was a French astronomer and mathematician Italian origin.
Life
Cassini was born in Perinaldo (Liguria ). He married the rich wife Geneviève de Laistre, was a French citizen in 1673 and began to write his first name Jean -Dominique. Two years before his death he went blind. He died at the age of 87 years. He was buried in the Paris church of Saint -Jacques- du-Haut -Pas.
Work
Cassini studied at the Jesuit college in Genoa and Bologna. He was executed in 1650 the successor of Father Bonaventura Cavalieri at the University of Bologna as professor of astronomy and mathematics through the influence of former general and former senator Cornelio Malvasia. There he taught Euclidean geometry, and - the doctrine of the Catholic Church in accordance with - the Ptolemaic astronomy. So he preferred long as the geocentric model of Tycho Brahe, while he hesitated to accept the heliocentric of Nicolaus Copernicus.
Cassini became a perennial, very accurate observer of the sky. 1655 he appointed his Meridiana in the cathedral of San Petronio in Bologna, the inclination of the earth's orbit, the solar diameter and the refraction of light in the atmosphere. He published his results quickly in 1662 in tabular form. In addition, the telescopes of Eustachio Divini (1610-1685) and Giuseppe Campani (1635-1715) got him on spectacular discoveries: With the help of the Great Red Spot on Jupiter Cassini certain its autorotation ( 1665). He also calculated the rotation period of Venus, Jupiter and Mars and examined the surfaces of the planets accurately. For navigation, the regular circulation of Jupiter's moon Io should serve as a celestial clock to determine longitude. These Cassini issued in 1668 detailed tables ( ephemerides Bononienses mediceorum siderum ). It earned him a reputation in 1669, which was established just by King Louis XIV Academy of Sciences in Paris.
As director of the observatory Cassini proven itself to be determined by far-sighted planning of expeditions with the aim of the exact shape of the earth, to create an accurate map of France and to measure the solar system. He discovered more moons Saturn ( 1671 Iapetus and Rhea 1672 ) and in 1675 for the first time the gap in Saturn's rings, now called Cassini's division. Cassini observed periodic changes in the brightness of Iapetus. He realized that the moon Saturn always shows the same side, that rotates as the Earth's moon bound. In addition, he described in 1683 the zodiacal light.
Cassini interpreted the 14 then known celestial bodies (6 planets and 8 moons ) as a glorification of the Sun King Louis XIV It is believed today, Cassini had concealed out of reverence for his royal employer long that he had now discovered with Dione and Tethys, two other moons of Saturn. It was not until 1684 he announced the discovery.
The survey in France by means of triangulation was to the chagrin of Louis XIV a significantly smaller area of his empire than previously assumed.
Cassini rejected the findings of Jean Richer and Philippe de La Hire to Earth flattening at the poles, the predictions of Isaac Newton and Christiaan Huygens had been confirmed by the to 1683. He imagined a flattening at the equator, as well as later, his son and his grandson.
Richer determined in 1672 in Cayenne, together with Cassini in Paris the distance Earth - Mars. This Cassini calculated parallax of the Sun of 9.5. " This could be the first time the distance Earth-Sun, today the astronomical unit, and use it to specify all the distances in the solar system. Yet the measurement accuracy was not sufficient (the value was up by 7 % low), so Cassini's result by many, particularly by Edmund Halley was not accepted.
1676 formulated his staff Ole Rømer the hypothesis that the speed of light must be finite. Cassini initially agreed and disagreed then, because he was a follower of the prevailing assumption of instantaneous propagation of light, which goes back to René Descartes.
His conservatism is also made clear that he rejected the elliptical orbits of Johannes Kepler and the theory of gravitation of Newton. Instead of ellipses he hit 1680 before a curve of the fourth order, which is now called the Cassini ovals or Cassini oval.
For the lunar orbit in 1693, he formulated three laws Cassini:
Cassini's successor as director of the Paris Observatory were his son Jacques Cassini ( Cassini II), and his grandson César François ( Cassini III) and his great-grandson Jean Dominique ( Cassini IV).
Cassini particularly Jean -Baptiste Joseph Delambre brands rightly regarded as a traditionalist. Nevertheless, he is considered one of the most important astronomers in the 17th century.
After him the asteroid ( 24101 ) Cassini was named and the lunar crater after him and Jacques Cassini Cassini.
Writings (selection )
- Some Observations Concerning Jupiter. Of the Shadow of One of His Satellites lakes, by a Telescope Passing Over the Body of Jupiter. In: Philosophical Transactions. Volume 1, Number 8, January 8, 1666, pp. 143-145, doi: 10.1098/rstl.1665.0067.
- A Discovery of Two New Planets about Saturn, Made in the Royal Parisian Observatory by Signor Cassini, Fellow of Both the Royal Societys, of England and France; English't Out of French. In: Philosophical Transactions. Volume 8, 1673, pp. 5178-5185, doi: 10.1098/rstl.1673.0003 (full text).
- An Extract of the Journal Des Scavans. of April 22 st. N. 1686th Giving an Account of Two New Satellites of Saturn, Discovered Lately by Mr. Cassini at the Royal Observatory at Paris. In: Philosophical Transactions. Volume 16, 1686, pp. 79-85, doi: 10.1098/rstl.1686.0013 (full text).