First of all, keep in mind there aren't many jobs in astronomy if you don't have a PhD in the subject. It's more important that you go to a top grad school than a top undergrad school, but if you can get into both, great. You'll want to major in physics and take courses in astronomy, math, and computer science. Astronomy is good to have when applying to grad school in astrophysics, but physics is essential. Spend your college summers doing research at your school and others (look up REU programs) to get experience for grad school and to make sure you really want to do research for the rest of your life.
Great schools for astronomy and physics include Harvard, Berkeley, CalTech, UCLA, Columbia, Cornell, Yale, Princeton, U Chicago, U Arizona, UC Santa Cruz, U Washington (state), Purdue, UMass Amherst, U Hawaii, U Virginia, U Wisconsin, UNC Chapel Hill, Ohio State, U Toronto, and others. Also, you can study physics at pretty much any college or university, including liberal arts schools, and still get into a top grad program.
Arizona State is a decent program but definitely not in the top 20, and MIT doesn't actually offer much for astrophysics (but would be a good undergrad physics school).
