There is a specific phobia called selenophobia which is the fear of the moon or moonlight amongst individuals. This type of phobia is also called lunaphobia and is related to the fear of a full moon, which is called remaphobia. Now the reason this fear can exist in a person can vary on a person and what they have experienced in their lifetime. This type of phobia is specific and isolated and it is not something that you simply develop without reason. As a non social phobia, the entire thing is based some sort of previously trauma that a person may have experienced, especially at a younger age. The trauma has been most likely, but not necessarily, a physically injurious event and has shaped the idea in a person’s head about the phobia.
With regards to the moon it could be because the moon signifies the night time which is often a time when crime rates go up a lot. On the other hand it could be something like a person’s feelings that were put in place by their parents after regular warning s of not going out after dark or being taught to be afraid of the night time because of the dangers it poses to the person.
A lot of people who have this phobia have also seen the idea reinforced in their head by events that may have happened to people who are close to them. The idea of the night time being dangerous or a fear of bad things happening when the moon is around can be reinforced by simply knowing about another person who may have gotten assaulted or mugged during the night time. The idea of the fear of the moon when it is full can also be reinforced in a similar manner amongst people.