A spectacular display of Aurora Borealis or the Northern Lights over Lapland, northern Sweden. When aurora is very active it often displays its most beautiful form known as aurora corona. It appears near the zenith. Its form can appear to boil with motion, its colors can range across the entire spectrum and, when bright, it can easily cast a shadow. Aurora is produced by the collision of high-energy charged particles, originated from the sun, with atoms and molecules of Earth’s atmosphere (at altitudes above 80 km). The vivid green and purple auroral colors are caused by high atmospheric oxygen and hydrogen reacting to a burst of incoming electrons.