[pi-squared]

Using the right-hand rule: knowing the direction of spinning, if you point your thumb up and wrap the other four fingers in the direction of rotation, the thumb will be pointing North. Oposite of that is South. East can then be defined along the direction of spinning (eastward or counterclockwise looked from North, the way Earth is spinning) and West - opposite to that, clockwise looked from North, opposite the direction of rotation.