What exactly are the differences between Astronomy, Astrophysics, Cosmology, Planetary Science?
The line is blurring between astronomy and astrophysics. Schools offering both don't require quite as much math and physics for the astronomy majors as they do for the physics majors. People are working as astronomers with PhDs in astronomy, astrophysics, and physics. Some ways of studying astronomy require a bit more math and physics than others, so those would be closer to physics or astrophysics than astronomy. But there doesn't appear to be a clear divide.
Planetary astronomy and cosmology are subfields of astronomy/astrophysics that you can studying with a degree in astronomy/astrophysics/physics. Other fields include solar physics, galactic astrophysics, and stellar astronomy. But you can approach any of those from more of an astronomy viewpoint (describing observations), or a physics viewpoint (modeling systems, theory) or a combination of the two. And then each of those subfields have more specific fields of study, and then there's the wavelength regime you're interested in (radio, optical, gamma ray, etc) and then there are already dozens of people doing just that.
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