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.
3. Reykjavik, Iceland. This beautiful area is located on the very edge of the Arctic Circle. While Reykjavik offers one of the most accessible ways to see the Northern Lights, transportation to and from Iceland can be difficult, especially during the winter season when the Northern Lights are most prominent.