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.
Northern Lights Iceland when to go. northern lights iceland when to go is the big question. These lights are like green, blue, pink and purple curtains, moving high up in the sky with a magical glow. It is one of the wonders that nature offers us.