What is the largest gap in Saturn's rings, discovered by Giovanni Cassini?

The largest gap in Saturn’s rings, discovered by Giovanni Cassini, is the Cassini Division.

The Cassini Division is the broad, dark separation between Saturn’s B Ring and A Ring. It is about 4,800 kilometers wide and appears from Earth as a prominent black band, although it is not completely empty. Spacecraft observations revealed that the division contains faint ring material and numerous narrower gaps and ringlets.

Giovanni Domenico Cassini identified the separation in 1675 while observing Saturn from the Paris Observatory. His telescope had a 2.5-inch objective lens, a focal length of about 20 feet, and roughly 90× magnification. The feature was later named in his honor.

The Cassini Division is technically a division rather than a narrow gap: planetary-ring nomenclature generally uses “division” for a broad separation between named rings and “gap” for a narrower opening within a ring. The Encke Gap and Keeler Gap are narrower features within the A Ring, while the Roche Division lies farther outward.