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.
Northern Lights Iceland best time: more details. The northern lights are a result from emission of photons in the highest altitude â more than 80km up, made by ionized nitrogen regaining an electron, and oxygen and nitrogen atoms coming from an excited level to a more grounded state.