Giovanni Cassini discovered Saturn moon Iapetus on October 25 in 1671

French-Italian astronomer Giovanni Cassini discovered Saturn's moon Iapetus on October 25, 1671, Astronomy Magazine and Space both reported. Cassini observed the celestial body using a 34-foot Campani refractor telescope, according to Astronomy Magazine. [1][2]

Cassini had arrived as director of the under-construction Paris Observatory in 1669, Astronomy Magazine reported. He persuaded the finance minister of King Louis XIV to purchase the Campani refractor telescope that enabled the discovery. [1]

Iapetus is the outermost of Saturn's large moons and the third-largest moon orbiting the planet overall. It has an estimated diameter of 1,469 kilometres, making it the eleventh-largest moon in the Solar System. [3]

Astronomers call Iapetus the yin-yang moon because of its extreme contrast in surface brightness, Space reported. The leading hemisphere, Cassini Regio, is dark and reddish-brown, while the trailing hemisphere, Scandia Regio, remains bright and icy white. A massive equatorial ridge up to 20 kilometres high also runs along the moon. [1][2][4]