For example, UC Berkeley offers an astrophysics MAJOR under the title BA degree and also offers a physics MAJOR under a BA degree. Does that mean that these are two different majors with two different degrees?
You are awarded a degree by your college (for undergrad generally a bachelors degree – BA is Bachelor of Arts, BS is Bachelor of science). And for your degree you must declare and complete a major which is the particular area of concentration you took up for your degree.
So a degree is like an umbrella for specific majors/minors?
Yes. You can get a BA in a host of majors. BA in English. BA in History. BA in Physics, etc…
A Bachelors is the level you reached and completed. A major is the particular subject matter. I think what’s confusing you is that some science or math topics can be either a BA or BS.
Look at the dept descriptions of different programs and the classes they involve.
Another way to think of it—your major is the area of study, and so can be at any level. For example, you can get a BA degree with a major in English, and then get an MA degree with a major in English.
In order to be awarded a degree in whatever, a college requires you complete certain courses and/or a number of units. These courses/unit reqs will come from one’s “major” area of study (eg physics), but also come from completing a school’s GE reqs, or from other courses of a student’s choosing. If one satisfactorily completes the requirements of one’s major and any other school reqs (eg GE reqs or completion of a certain number of units), then one is awarded a degree. Your diploma will reflect that your degree is in whatever you majored in.
Astrophysics sounds like one degree and physics sounds D’s like a different one. Look at the requirements for each one. They’re probably different.
For a science subject you usually want to go for the BS rather than the BA, not that employers will be breaking down your door to offer you a job in either case.