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.
The Northern Lights, or Aurora Borealis, are one of Icelandâs most famous attractions. These beautiful green (and sometimes white, pink and purple!) lights dance around the sky in Iceland quite frequently â but can only be seen in the wintertime.