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.
Best month to see northern lights - Reykjavik Forum. Best month to see northern lights. Which Reykjavik hotels are on sale? I'm thinking of taking my wife to see the auroras for her birthday, obviously doing a bit of homework to to maximise our chance of success as I realise nothing is guaranteed.