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.
Winter is the best time for viewing the northern lights, since darkness is a must. August through mid-April of 2012-2013 has been an especially good season for viewing. This is because we're coming close to an 11-year peak in sunspot activity, which means lots of solar wind.It's not too late -- the peak isn't over.celand is one of the world's most accessible spots for viewing the northern lights, making it one of the country's top tourist attractions. Capitalizing on its mystique, enterprising Icelanders have designed borealis-oriented cruises, overland tours, and even a concept bar at far-flung Ion Hotel.