One of the goals for my game is to have planets rotating on an axis and orbiting a star. I’ve got a version of this working, with entities on the planet adhering to its rotation and orbit. Given the camera being locked to a position on a planet, this results in a day/night cycle. I’ve added increased brightness when the camera is directed towards the system’s star.

Flying around a planet results in gravitational capture when close enough. This means that the spaceship effectively enters geostationary orbit, and any manoeuvres are relative to the planet rather than absolute coordinates.