To be fair I had advanced warning about the uselessness of certain majors. A young journalist told me when I was studying that her major was in Communist societies. And that she knew it was useless once she saw the Berlin wall fall.

Regarding Astronomy, I think it is like Economics. You do lots of maths so that you can do something people understand (Typing commands into the telescope or explaining certain points.) Then you go back to doing lot of maths.