You need to take everything that physics majors take in college. Only ingraduate school does your program look different. Undergraduate coursesmust be selected from the advanced courses in physics and mathematics. You also need advanced statistics under your belt. You probably do not have to take any of the topology courses in the math department, but all of thecalculus and advanced math courses for physicists and engineers should be taken, and in physics..well...there is no such thing as not taking enough physics. You must also do at least B-level work or better in all of the courses you take. There is a reason why there are only 6500 professional astronomers in the USA, and why only 100 PhDs are granted each year, despite the fact that EVERYONE is interested in the stars! Here is a plot of the membership to the American Astronomical Society to give you another perspective:

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