Ph.D. Student in Political Science at Harvard University
I actually think there is a lot of overlap in what types of classes you would want to be taking at the high school and college level. Both astrophysics and medicine require a lot of science knowledge, so you would be smart to fill up on things like chemistry and physics. Getting involved in science activities would also be a good idea. I know there are plenty of summer opportunities to work in labs and do research. A difference between the two disciplines is that astrophysics requires more math. To actually be an astrophysicist, you will need a Ph.D. The nice thing is that there is enough overlap so that you don't need to decide right now. Many people get a Ph.D. in subjects they didn't major in (me, for example), and pre-med classes usually do not take up your entire college schedule. Because of this, in college you could definitely take pre-med classes IN ADDITION to whatever you are majoring in, and later decide whether to go to graduate school for astrophysics. At a lot of schools medicine isn't even its own major.