The astronomical study of the planet Saturn.
The study of the planets is generally named after Greek gods, while the planets themselves are generally named after Roman gods. Saturn, the Roman god of agriculture, corresponds to the Greek god Khronos (or Cronus or Khronys), who was the father of the gods until Zeus dethroned him.
The word kronology isn't in common usage today, and is likely to be found only in collections of curious words or in works of science fiction.
Not to be confused with chronology, the study of time, or koniology (AKA coniology), meaning the study of dust in the atmosphere.