Why has horatio been asked to join the soldiers in the night watch what has he decided to do?

Here is the answer to the given question above. Horatio has been asked to join the soldiers in the night watch and what he has decided to do is that, they have seen a ghost of King Hamlet and want to let him know. In addition, he is Hamlet confidant and they want Horatio to believe that King Hamlet's ghost is definitely appearing. Hope this answers the question.