What should my focus be for my Math degree, if I want to go into Astronomy?

I have just enrolled in a bachelor's degree - a B.S. in Mathematics. Eventually I would like to get my Master's in Astronomy (or Astrophysics), or possibly Physics or Aerospace. What should be the focus of my B.S.? What types of cles should I take? Or should I simply take every Math cl I can get my hands one (which was my plan in the first place)?