I am following these instructions on measuring crater height in my own moon images: http://www.astro.ex.ac.uk/obs/experiments/lunar/script.html
They require me to calculate the sub-Earth and sub-Solar points on the Moon when the image was taken. Is there a way to do this in Skyfield? I can only find reference to this being done for sub-Solar points on the Earth using pyephem.
The Skyfield documentation describes getting the lunar longitude and latitude of the sub-Earth point here:
https://rhodesmill.org/skyfield/planetary.html#computing-lunar-libration
It looks like if instead of (earth - moon) you also did the same thing but with the difference (sun - moon), you would get the sub-solar point on the Moon. I’d suggest trying each of those out, and seeing if the values you get back match example values from some other authority you could check against to make sure you're getting values that mean the same thing.
(And, if that approach works, let me know by responding here with a comment, and I'll update the documentation to add a heading to that page of the docs that explicitly mentions the word “sub-Earth point” or “sub-solar point” — since I don’t think the word “libration” makes it obvious to folks needing sub-points that the section will answer their question.)