FAQ Is AST191 a prerequisite for AST192? No. You do not have to take AST191 before taking AST192. Some students will take AST192 first, and then take AST191 later, if that better suits their schedules. The two courses are independent. What is the difference between AST191 and AST192? The two courses cover different topics in modern astronomy. AST191 focusses on the Sun and the planets, asteroids and comets that orbit it. AST192 focusses on how stars work and on how matter is organized in the Universe. Is AST192 more difficult than AST191? No. Both courses are aimed at aquainting non-science students with the basic processes of scientific exploration. Of course, some science students may enjoy the courses as well. Why are there two different textbooks? You are only required to buy one book. The publisher makes two different versions, one which contains info on planets that we will not cover (but is used in Ast191) and a shorter version that omits that info. Buy whichever one you prefer!