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 to see the Northern Lights from anywhere around or above the Arctic Circle (which lies near the towns of Rovaniemi and Bodoe) bodÃ¸ is any time Between september and Late. April'you ll experience long winter nights. herehe optimal time of night for the Northern Lights is 11 p.m. to 2 a.m. Keep in mind that most visitors head out to begin their watch around 10 p.m. and conclude their night around 4 a.m., since the Northern Lights can be hard to predict (just like the weather in Scandinavia).