Click HERE to see all the data files I have collated and used in my coding activities along with .txt files explaining their contents.
This GitHub directory includes links to some data too large for GitHub, large data is stored on my Google Drive. Some activities have extra data files which download at runtime. Some FITs image data is available via links on this website under Resources -> FITs Processing.
There is a great list of astronomical data sources HERE by the Smithsonian Astrophysical Observatory.