Engraved copy of an oil painting of Cassini. The newly built Paris Observatory is depicted in the background.

The Contributions of Astronomer, Engineer and Mathematician, Giovanni Domenico Cassini (1625-1712)7

Cassini is one of the most important seventeenth century observational astronomers after Galileo and Kepler. He was born in Perinaldo, now a part of Italy, in 1625. Cassini’s fascination with astrology in his early years later developed into an interest in astronomy. He was employed by a wealthy marquis as an astronomer in Bologna. Here, he was able to use cutting-edge instruments to observe the skies. His work demonstrated his talents for precision and clarity which would later earn him positions in academia.


When Cassini was 25, the University of Bologna made him a professor of astronomy. In 1669, at the invitation of King Louis XIV of France, Cassini became a part of the Royal Academy of Sciences in Paris where he helped design the Paris Observatory. Cassini would not return to Italy, and he became a French citizen in 1673, changing his name to Jean Dominique. Although he made significant contributions to science in Italy, he made even greater ones during his life in France. He discovered four of Saturn’s moons and discovered the gap between the rings of Saturn, which is now called the “Cassini Division” in 1675. He also discovered Jupiter’s Red Spot, independently of Dutch physicist and mathematician Christiaan Huygens. His observations of spots on the surface of Jupiter allowed him to measure Jupiter’s rotational period.


In 1666, after similar observations of Mars, he calculated a value for the rotational period of Mars. Two years later he compiled a table of the positions of Jupiter’s satellites, which was used in 1675 by the Danish astronomer Ole Romer, who established that the speed of light is finite. Cassini also measured the size of the solar system by using the distances of each object from Mars.


In engineering, Cassini wrote several works on flood control, and he used a wide range of experimental techniques in applied hydraulics. He also began work on a project to create a topographic map of France in the 1670s, which was the first topographic map of an entire country.   


Cassini died in Paris, France in 1712, after making many significant contributions to astronomy. In 1997, NASA and the European Space Agency (ESA), launched the Cassini-Huygens orbiter and space probe. The mission proved successful and uncovered the wonders of Saturn and its moons. In 2017, it made its final mission and plunged into Saturn’s atmosphere, sending back to Earth amazing information along the way! 


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