You need algebra and calculus...complete mastery not just the BELIEF that you know this material...for every area of astronomy. For theoretical work you need even more mathematics including Tensor Analysis if you are going into cosmology or general relativity among other topics. You may not need these every day if you are an observational astronomer working with taking data and analyzing it, but a knowledge of calculus HAS to be right there at your finger tips because there are times when you need to use it for calibration work and comparing your data with theoretical expectations. Algebra is a work horse because you are never really very far from having to manipulate quantities in a way that you learned in algebra.
I know of no astronomers who did not excel in algebra and calculus...getting mostly As in both forms of mathematics.
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