Most folks in the postdoctoral track will not get research jobs. They either leave astronomy or take jobs whose primary duties are related to teaching. The teaching load at most colleges is so heavy that only the most persistent continue to do any significant amount of research. If their main focus always was on teaching, then they may be able to go straight from graduate school to such a position.

Almost everyone who goes into research or teaches at a University or major 4-year college has a Ph.D. A Ph.D. takes about 6 years of work after a B.S. in astronomy or physics. You have to be seriously dedicated to this profession; it is unlikely that you will make up the 10 years of lost earnings from graduate school and postdoctoral positions during your career.

There are positions at 2-year colleges and, perhaps, a few at 4-year schools for folks with only B.S. degrees. The difficulty here is not that a B.S. is insufficient background for teaching introductory classes in astronomy but that there is a large pool of Ph.D. astronomy graduates who are also vying for these positions.

Some folks with a B.S. degree, or even less, sometimes find positions as technicians, night assistants, or observers. A few of these have become quite famous for their work or discoveries but the pay for such jobs is not very high.