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 In Iceland Guaranteed darkness is the first important factor. The best season to see the northern lights in Iceland is from September to mid-April â these are the months where there are full dark nights. Some sources will recommend November to February, as they are the darkest months with the longest possible window to see the lights, however these sources often fail to take into account that these months can have the worst weather with lots of rain and snow.