Cosmology
Cosmology is one of the more far-flung parts of astronomy. It can basically describe the entire universe, its history, and its future (within reasonable approximations). However, cosmology has been mostly split into 2 parts: shallow popular science "oh the universe is big and we're small" and straight general relativity (GR). These sections should traverse the middle ground of math, but also including parts from both sides in hopefully reasonable amounts.
And of course:
mr yuen
teaching GR to year 1s is like creating the Torment Nexus from the book "Don't Create the Torment Nexus"
Danger
the entirety of cosmology is a WIP