Astronomy is a difficult science because astronomers are trying to understand the nature of the Universe, but for those who like to be challenged, it can be endlessly rewarding. Students who excel in math and science have the best chance of excelling in a career in astronomy. Chemistry and physics will also provide a strong background for the astronomer. Students who are interested in astronomy as a career should seek involvement in local science groups or astronomy clubs. A list of astronomy clubs in the United States can be found here: http://www.astronomyclubs.com/1/190/0/0/select_state.aspx
In college, a science major will be desired, with a strong emphasis in math and science. In general, a student planning to do graduate work in astronomy should have taken physics courses covering electricity and magnetism, atomic and nuclear physics, thermodynamics, statistical mechanics, and quantum theory. For some astronomy specialties, though, studies in geology or chemistry may be the focus. Additionally, since technology plays such a crucial role in science today, a good grounding in computer science will be helpful for astronomy students, especially those considering a specialty in theoretical astronomy. Finally, all good scientists need the ability to read and write clearly, so as to communicate to others the difficult concepts they encounter.
Most astronomy positions require a Ph.D. degree, which requires five or six years of graduate work. Admission to graduate schools generally requires completing an undergraduate physics or astronomy/physics major with at least a B average and acceptable scores on the Graduate Record Exam (GRE). Graduate astronomy students will take advanced courses in astronomy and astrophysics, while beginning research. The specific courses a student will take depend upon his interests and the requirements of the department.