Mechanics and astronomy used to be small majors, so it was inconvenient to start classes. The main course content is a lot of mathematics, so it is often combined with mathematics department. Small departments will be independent when they grow up, although they often take classes with the math department. At present, it is generally a department structure, and such a department name is rare. For example, the Department of Mathematical Mechanics in Peking University, 1974 is independent.