S wave -- a shadow zone appears when the velocity suddenly decreases 103-180 degrees from the epicenter. Describe the differences between P and S waves. P waves expand and contract, can move through liquid solid and gas. S wave moves up and down or side to side moves through only solids.
Optimal conditions to see the northern lights in Iceland is when skies are clear and dark (away from the city lights, in cold temperature and ideally from mid-September to mid-April.
THE BEST TIME TO GO. The best time to see the northern lights in Iceland is from early September to mid-April as that is the time we donÂ´t have the 24 hour daylight as we do in summer. If you are lucky you can even see them late August even though the northern lights season hasnÂ´t formally begun.