First grade. According to official website of Nanjing University, interesting astrophysics is the main part of elementary mathematical astronomy, an elective course for first-year undergraduates in the School of Astronomy and Space Sciences of Nanjing University, and an important part of the core course of stellar structure and evolution for graduate students. It involves some essence of astrophysics, and makes full use of dimensional analysis, qualitative and semi-quantitative research methods. Nanjing University, located in Jinling, the ancient capital of Zhong Ling, is a century-old prestigious school with a long history and outstanding reputation.