I definitely agree with Barry and Dante. The obsession of astronomy is what drove the narrator to insanity. In Dante's blog, this was one of the questions that he asked and it was not answered, but through the story everything that happens deals relates to his astronomy somehow.
In the beginning of the story, the narrator explains himself as having obsessive-compulsive disorder. From the way that he explained his disorder we know that this diagnosis was completely correct. The narrator questions the diagnosis, researches the diagnosis and then completely rejects its, stating that he will not receive the help he needs until he disproves the diagnosis. After reading the story, the questioning of the diagnosis did not seem like a bad thing after all.
The desire of knowledge for the narrator, which is a much nicer word that insane, ultimately leads to his demise and his best friend's demise. To have to thought of drugging your friend and questioning him about astronomy is insane. To do all of this, after catching your friend in bed with your wife is another thing. I may be only person to think that this was the point in the story where his insanity peaked. But to catch someone in bed with your wife and the only thing you want to do is question him is not insane, I'm not sure what is. I guess scientist do really go after their questions.