The Moon is subject to four types of libration. Which of the following is NOT one of these types of libration?

Correct Answer: Option C — Vertical libration

According to Bowditch, the Moon's librations consist of libration in latitude, libration in longitude, and diurnal libration. These allow observers to see slightly more than 50 percent of the lunar surface over time. Vertical libration is a fictitious term and is not recognized among the four actual libration types.