When loading or creating a world with version 1.0.1 of astronomical, Minecraft will freeze to the point of being unable to close it at all (even by ending it in task manager).
This behavior occurs with or without an internet connection, and with or without performance mods installed.
The log is spammed with IllegalStateExceptions:
https://paste.atlauncher.com/view/0ea4b6d9-4fad-4673-a293-ff22f2bcfafd