The name given Saturn, the last of the planets visible to the naked eye to be acknowledged as a planet, is a puzzle. In mythology, Saturn was the god of agriculture; the connection between that entity and the planet Saturn remains obscure, unlike the connection between Mars, the god of war, for example, and the so-called Red Planet, Mars. A clue to Saturn's name may lie in the Assyrian word for Saturn: lubadsagush, which translates to oldest of the old sheep, possibly a reference to Saturn's slow movement through the sky. The Latin name may reflect an association between the planet's slow pace and that of grazing or plowing farm animals.

Italian Jesuit Francesco Maria Grimaldi first noted a key characteristic of the planet in 1645 when he estimated the difference between the planet's polar and equatorial diameters. Saturn is a flattened appearance, and Grimaldi's ratio reflected this: the...