The astronomical study of Venus.
The study of the planets are generally named after Greek gods, while the planets themselves are generally named after Roman gods. Venus was the Roman goddess of love; Aphrodite was the Greek goddess of love. But "Aphroditology" doesn't quite sound right.
When Aphrodite first emerged from the sea, the Zephyrs carried her to Cythera (or possibly Cyprus). Hence she is often referred to as Cytherea (or Kypris). And hence, cytherology.
The word cytherology isn't in common usage today, and you are unlikely to find it outside of collections of odd words and old science fiction stories.