Algorithms from "Practical Astronomy with your Calculator or Spreadsheet" by Peter Duffett-Smith. API documentation is published here.
If you're interested in this topic, please buy the book! It provides far more detail and context.
All spreadsheets and macros from the book, implemented in Python 3. (See details in lib/README.md)
The Python 3 implementation is intended as a learning tool. The code is easier to read and understand, but won't hold up as well where speed is required. So, the next step will be re-implementing the Python code in Rust. You can follow that work in the rust-implementation branch.