[Rich]

Things would make so much more sense if X was up and Y was right. Once you've established your Pole Star its easier to reference that than get the Sun's position at Sun rise on the equinox. So north would be the first dimension positive. If you make East your second dimension positive, then north is at an angle of 0 degrees, zero hundred hours is at 0 degrees, East is 90 degrees and angles are clockwise.

It strikes me that our world is irredeemably messed up. Which way should you wind your front facing triangles. there's just no right answer.