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.
So the short answer is no â you canât see the Northern lights in summer in Iceland. The long answer though is that it depends on how you define summer. Although the last northern lights tour is on April 15th and they donât start again until September 15th it doesnât mean that itâs impossible to see the lights outside of that time.