As you can see, nothing in Vue faces the same way. :/ This shows the Top World View and how things orient around the horizon. Camera north is 180 degrees roll, while Azimuth north is 90 degrees. The Sun Light controls/is controlled by the Azimuth and Declination. But when Azimuth is 0, the Sun Light's Roll is 90. Similarly, Declination 0 is Sun Light Pitch 90. (Also note: Declination 0 centers the sun on the horizon.)
The material Azimuth points the second material north at 0 degrees. These settings are the same for World Orientation or Object Orientation, when the object is zeroed. When you rotate the object with Object Orientation, the material split will move with it.
So what's it all mean? Well, if you want an object with moss growing on the north side, with sunlight from the east and the camera in the south facing north.... The material azimuth should be 0 (if the moss is material 2), the sun's roll should be -90, and the camera's roll should be 180.