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.
Although it would be great to easily pinpoint a how to see them, there are a lot of variables to consider for seeing them: season, weather, length of stay, location and luck. Of course, there are lots of fantastic things to do in Iceland and itâs always best to think of seeing the northern lights as an added bonus. So e.g. plan your trip with unique experience like The Aurora Bubble and The Aurora Floating tours. You will come back happy even if you did not see any northern lights dance.