Giovanni+Cassini

Italia Ieraci

**Giovanni Domenico Cassini**

Something that we as humans have never been able to fully understand is astronomy. According to John Millis, astronomy is the scientific study of all objects beyond our world. (1. Mills) Individuals who help us to understand this are astronomers. One astronomer in particular that has made a significant contribution to the field of astronomy is Giovanni Domenico Cassini. Actually, Cassini has many different names. The name Giovanni Domenico Cassini was given to him by his parents when he was born. When he moved to France, he also used the name Gian Domenico Cassini or Jean Dominique Cassini, which is the French version. (2. O'Connor) 

**Giovanni Domenico Cassini** was an Italian/French mathematician, astronomer, engineer, and astrologer. He was born on June 8th, 1625 in Perinaldo (at the time it was in the Republic of Genova) to Giacomo Cassini and Julia Crovesi. (3. Giovanni) His father was a Tuscan and his mother was the daughter of a Notary Public. Cassini was not brought up by his parents, but by his mother’s brother, Antonio Maria Crovese. Crovese was Giovanni Cassini’s first tutor. This situation most likely impacted his thinking on the world and life. Cassini’s first interest was in astrology rather than astronomy. He read widely about this topic and soon was very knowledgeable, yet was convinced that there was no truth in astrological predictions. What was odd though, was that through his knowledge and research on astrology, he was offered a position in the Panzano Observatory in 1644. This position allowed for him to learn from two brilliant Jesuit scientists, Giovanni Battista Ricciolo and Francesco Maria Grimaldi. In 1650, Giovanni Cassini became a professor at the University of Bologna and became, in 1671, director of the Paris Observatory. Through all of Cassini’s work, we can see that he believed in an Earth centered solar system. An example of this would be with the comets. These comets which are beyond Saturn, he felt originally came from Earth. Some proposed models that Giovanni Domenico Cassini accepted were Tycho Brahe and Copernican. (2. O'Connor)

Giovanni Cassini made several important discoveries early in our solar system. The first person to observe the rings in 1610 using his telescope was Galileo Galilei. Although he was unable to identify these rings, it allowed for Giovanni Domenico Cassini to begin. Cassini was actually the first person to discover that there were spaces between the rings of Saturn in 1675. This gap he discovered between the A ring and B ring is still known today as the Cassini Division. These are the densest parts of the Saturnian ring system. This ring system is “the most extensive planetary ring system of any planet in the solar system. They consist of countless small particles, ranging in size from micrometers to meters that form clumps that in turn orbit about Saturn. The ring particles are made almost entirely of water ice, with some contamination from dust and other chemicals.” What many do not realize is that Saturn’s rings are old, dating to the formation of Saturn. What fools many people, is the brightness and purity of the water ice on the rings.(4. Rings of Saturn)  He also studied extensively the moons of Saturn, discovering four of them himself. Cassini discovered Lapetus in 1671, Rhea in 1672, and Tethys and Dione in 1684. Lapetus is the third largest moon of Saturn and the eleventh in the solar system. This moon is best known for its dramatic ‘two-tone’ coloration, but recent discoveries by the Cassini mission have revealed several other unusual physical characteristics, such as equatorial ridge that runs about halfway around the noon. (5. Lapetus (moon)) Rhea is the second-largest moon of Saturn and the ninth largest moon in the Solar System. It is an icy body with a low density. (6. Rhea (moon)) Tethys is the 16th largest moon in the solar system and is more massive than all known moons smaller than itself combined. It is an icy body similar in nature to Dione and Rhea. (7. Tethys (moon))

Cassini was the first to accurately measure the rotational period of Jupiter at nine hours, fifty-six minutes. In 1664, Robert Hooke discovered the Great Red Spot of Jupiter and Cassini used his own observations to determine the measurement in 1665. During his Jupiter observations, he also cataloged the movements of all Jupiter’s moons and noted the differential rotation of Jupiter’s atmosphere. Cassini later was able to measure the rotational period of Mars. In 1662, Giovanni Cassini published accurate measurements of the sun’s motion through the sky and later he came within 7% of measuring the distance from the Sun to the Earth. Through triangulation, he also determined the distance to Mars. Cassini is credited with giving the most accurate dimensions of the solar system at the time. Giovanni Domenico Cassini contributed so much to astronomy that they even named a spacecraft (Cassini-Huygens spacecraft) and a mission after him. This spacecraft was launched on October 15, 1997 by NASA’s Jet Propulsion Laboratory from the Kennedy Space Center in Florida. After a seven-year journey, it entered Saturn’s orbit on July 1, 2004 Coordinated Universal Time (UTC), or June 30 at 8:36 p.m. MDT. The mission includes the Cassini orbiter, which will orbit Saturn and its moons for four years, and the Huygens probe, which was released from Cassini orbiter and landed on the Titan moon to explore its surface and surroundings. These instruments will provide scientists with new and exciting data to help understand the mysterious Saturnian system. (8. Cassini) 

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**References**

1. Mills, John. Astronomy-What Is Astronomy?- [] 2. O'Connor, J.J and E.F Robertson- Cassini biography- [] 3. Giovanni Domenico Cassini- [] 4. Rings of Saturn- http://en.wikipedia.org/wiki/Rings_of_Saturn 5. Lapetus (moon)- [] 6. Rhea (moon)- http://en.wikipedia.org/wiki/Rhea_%28moon%29 7. Tethys (moon)- http://en.wikipedia.org/wiki/Tethys_%28moon%29 8. Cassini- UVIS Mission to Saturn and Titan- []