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 official Aurora season in Iceland is from October till March but like with so many other things that have to do with Icelandic nature itâs not something you can say with any certainty. For example, the first Northern Lights of the season in ReykjavÃ­k this year were seen around the middle of August. The ideal conditions to see them are when itâs cold and dark outside and the Aurora activity is high. The cold per se is not an factor but the sky has to be clear which it usually is on very cold nights.