Near the surface of the Earth, the magnetic field is pretty closely approximated by a dipole field titled at an angle. Does anyone know of a theoretical reason for this, or is it just an observed fact (I'm guessing the former).
Also, could someone explain why the field from a solenoid coil is a dipole?
At the moment, my guess for the Earth's field question is something along the lines of the other non-dipolar parts cancelling somehow, or else just being too small at large distances.