A sky that belongs to the Moon
A lunar observer needs a lunar body-fixed frame, a local horizon and the Moon's rotation and libration.
Earth near the same sky region
For a fixed near-side observer, Earth stays around one part of the sky and moves modestly with libration. A far-side observer generally cannot see Earth. Earthrise and Earthset occur where location and libration actually permit them.
Time and orientation
UTC dates are converted by Astronomy Engine into its UT/TT time model. Geocentric J2000 vectors are differenced to form lunar observer directions, with an IAU pole and prime-meridian orientation. This is an educational approximation to a full relativistic lunar topocentric ephemeris.
Surface and horizon
Apollo region coordinates are sourced from NASA's NSSDCA Mean Earth/Polar Axis table. Their use with the IAU orientation is approximate. The foreground is a textured spherical horizon, not local LRO terrain. No atmospheric refraction is applied on the Moon.
Earth sky
Earth views use topocentric apparent planetary coordinates and optionally an atmospheric refraction model. Star positions use HYG catalog data with proper motion and precession. Weather, dust and light pollution are outside this model.