On Oct. 25, 1671, the Italian astronomer Giovanni Cassini discovered a new moon at Saturn! Iapetus was the second moon anyone had ever found orbiting Saturn, and it was the first of four moons Cassini would discover at the ringed planet.
The Dutch astronomer Christiaan Huygens had discovered Titan, the largest of Saturn's moons, about six years earlier. After Cassini found Iapetus, he also found the moons Rhea, Tethys and Dione.
When Cassini first saw Iapetus, the moon looked like a tiny speck on the west side of Saturn. He calculated its orbit and thought he would be able to see it again on the east side of Saturn 39 days later, but it was nowhere to be s...
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