|Diameter|| 1,436 km|
|Distance from primary|| 3,561,300 km|
Iapetus is the seventeenth moon of Saturn. The astronomer Cassini first viewed Iapetus with a telescope. The satellite was observed to "disappear" every 40 days, half of its 79-day orbit. Cassini noticed that the "winking" moon's entire hemisphere was vastly brighter than the other side and the moon was synchronously rotating.