... Bad Astronomy . ... Bitesize Astronomy . ... Have you ever looked at pictures of Saturn's rings and noticed what look like gaps in the rings? ... Gian Domenico Cassini discovered a large gap in Saturn's rings in 1675. Later, an astronomer named Encke discovered a smaller gap near the edge of the rings. ... It was found long ago that an orbit in the Cassini Division, as the large gap is named, has a period almost exactly one-half that of one of Saturn's moons named Mimas. ... 2008 Phil Plait. ...