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 order to see the Northern Lights, you need a dark, clear night. They are visible from late September to March anywhere from 6pm to 6am. There also needs to be solar flares on the sun or solar wind; the Aurora Borealis happens when particles from the sun enter Earthâs atmosphere and collide violently with gas atoms.