page_title: Giovanni Domenico Cassini
section_title: Time in Italy
hierarchical_section_title: Giovanni Domenico Cassini / Life / Time in Italy
caption_attribution_description: Osservazione del solstizio 21.06.12, fi,
context_page_description: Giovanni Domenico Cassini, also known as Jean-Dominique Cassini was an Italian mathematician, astronomer and engineer. Cassini was born in Perinaldo, near Imperia, at that time in the County of Nice, part of the Savoyard state. Cassini is known for his work in the fields of astronomy and engineering. Cassini discovered four satellites of the planet Saturn and noted the division of the rings of Saturn; the Cassini Division was named after him. Giovanni Domenico Cassini was also the first of his family to begin work on the project of creating a topographic map of France.
  The Cassini space probe, launched in 1997, was named after him and became the fourth to visit the planet Saturn and the first to orbit the planet.
context_section_description: Cassini was the son of Jacopo Cassini, a Tuscan, and Giulia Crovesi. In 1648 Cassini accepted a position at the observatory at Panzano, near Bologna, to work with Marquis Cornelio Malvasia, a rich amateur astronomer, initiating the first part of his career. During his time at the Panzano Observatory, Cassini was able to complete his education under the scientists Giovanni Battista Riccioli and Francesco Maria Grimaldi. In 1650 the senate of Bologna appointed him as the principal chair of astronomy at the University of Bologna.
  In San Petronio, Bologna, Cassini convinced church officials to create an improved sundial meridian line at the San Petronio Basilica, moving the pinhole gnomon that projected the Sun's image up into the church's vaults 66.8 meters (219 ft) away from the meridian inscribed in the floor. The much larger image of the Sun's disk projected by the camera obscura effect allowed him to measure the change in diameter of the Sun's disk over the year as the Earth moved toward and then away from the Sun. He concluded the changes in size he measured were consistent with Johannes Kepler's 1609 heliocentric theory, where the Earth was moving around the Sun in an elliptical orbit instead of the Ptolemaic system where the Sun orbited the Earth in an eccentric orbit.
  Cassini remained in Bologna working until Colbert recruited him to come to Paris to help set up the Paris Observatory. Cassini departed from Bologna on 25 February 1669.
caption: The pinhole-projected image of the Sun on the floor at Florence Cathedral. Cassini measured a similar image over a year at San Petronio Basilica to try to prove the Earth orbited the Sun.
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