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.
Report Abuse. If you want to see the northern lights, don't go In August. At that time of year, the nights are still too bright in Iceland for any northern lights to be seen. Mid-October to early November, on the other hand, is one of two periods of the year when the chance of seeing the northern lights is the greatest.rrespective of this, the northern lights are visible every winter in Iceland. Check out the Flickr pages I link to in source for examples of what you would be likely to see. Once in Iceland, be prepared to travel to whichever region has clear skies.