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 best time of year to spot the Northern Lights in Iceland is between November and March. GETTY. Iceland is a popular destination for hunting the elusive Northern Lights, but the land of frost and fire is also a great place for adventure sports and relaxation.. Search for the Northern Lights. Iceland is a great place to spot the lights but the conditions have to be right. Between November and March is the best time to see them, and you have more chance if you go at a time of the month when the moon is small.