Complex sentence: The Moiré effect creates arrows that'point' towards an imaginary line marking the hazard; as navigators pass over the hazard, the arrows on the beacon appear to become vertical bands before'changing' back to arrows pointing in the reverse direction.
Split into simpler sentences: The Moiré effect creates arrows that'point' towards an imaginary line marking the hazard. As you pass over the hazard, the arrows on the beacon appear to become vertical bands before'changing' back to arrows pointing in the reverse direction.