If you want to do celestial navigation based on the game then you need external planetarium software to properly get the altitude of celestial objects.
Years ago for SH4 6SJ7GT made a Python script that took the 0th waypoint coordinates out of a savegame file and converted it to real-world longitude and latitude coordinates. The script also asked the user for time and date to make a observation situation script for Stellarium. Then viewing the sky in the Stellarium software and recording the height angle (altitude) of several objects it was possible to make a fairly accurate position fix using an almanac and a calculation sheet covering the years of the war. The fix could then be plotted manually on the in-game map, or on a piece of graph paper.
As the coordinates in the planetarium give true stationary positions (refracted if configured right) it doesn't account for the wobblyness of a moving submarine deck while at sea. But you can always add your own random fudge-factors to it to make life hard on yourself.
http://www.subsim.com/radioroom/show...ght=Stellarium
It's probably not compatible anymore with the latest version of Stellarium. They changed the way to make handle situation scripts I think. Or the links to the web-based almanacs are dead I think. I didn't do this myself all that often to be honest. It turns out I'm a lazy navigator.