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.
In these far northern latitudes you can see the Auroral activity on a average 100 nights a year and the best time to see Iceland's Aurora Borealis is around midnight when Iceland's Aurora Oval is said to pass over the observer.nfortunately the Aurora Borealis isn't that predictable, having spent 5 weeks in Iceland and about 4 years in total in Norway, Sweden and Finland, the best time to see this phenomenen is obviously ONLY at night.