The stars or the earth are not the problem with celestial navigation in SH3 or 4. Sunrise and sunset are accurate to the time if you know at what coordinates you are. It's the measurement tools that fall short. Mods have been made to measure star and sun elevations above the horizon. Like what a sextant does. (very generally speaking) However they had nowhere near the accuracy or resolution as required to get your fix within a few minutes of arc. Also, there were some issues with the clock flipping timezones in odd locations and unstable behaviour with savegames. (but maybe that's just in SH3, I can't remember)
The 'best' solution sofar (imho) was by using an external planetarium program that displayed the heavens based on the players location in a savegame. But that requires getting out of the game, and obviously doesn't use the stars displayed in the game.
http://www.subsim.com/radioroom/show...ght=Stellarium