I'm starting my second year as an astronomy/physics double major. Up to this point, I've only had basic foundation courses, most of which I've come across in high school. I know this question is highly subjective, but when do the courses start to become really difficult? I've heard from TAs that the first two years are mostly foundational material and it starts getting "serious" around the junior year, is this true? However, the gpas of the courses in the junior/senior year are higher than the first two years; why is this the case? For example, I work with a first-year graduate student and, although I understand that he has had 3-4 more years of schooling than me, he seems to know a great deal about even the more specific aspects of astronomy. Any insight is much appreciated.