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 aurora is most active late at night or early in the morning, when the sky is clear and the air chilly. The best time to watch is in spring and fall, especially February, March, September, and October. One of the best times to look for the Northern Lights will be when it is dark because of a new moon.Hardy Alaskans like to put on their parkas and lie on their backs in the snow to watch. The best viewing happens outside of Fairbanks, away from the city lights.ne of the best times to look for the Northern Lights will be when it is dark because of a new moon. Hardy Alaskans like to put on their parkas and lie on their backs in the snow to watch. The best viewing happens outside of Fairbanks, away from the city lights.