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.
Icelandâs northern latitude means it experiences big differences between winter and summer daylight hours. From May to August, you wonât see much darkness and in the month of June the sun never fully sets in the north. Conversely, in peak winter expect only about four to six hours of daylight but the possibility of seeing the Northern Lights on a clear night. Spring and fall daylight hours are normal.