What is the theme in The Catalogue of the Universe by Margaret Mahy?

Unrequited feelings is a major theme in the story. Throughout much of their friendship, Tycho has had romantic feelings toward Angela. Angela, in turn, feels only friendship for Tycho. Tycho watches from the sidelines as Angela dates other boys, while he is left to pine for her affections. In a similar way, Angela feels affection (or at the very least curiosity) about a father she knows only through the stories her mother has told her. When she comes to her father Roland's office, full of expectation of the possibility of a relationship with Roland, his reaction is anything but warm and welcoming. He does not want to be in her life.