Aurora over Sweden

via NASA

"Image Credit & Copyright: Göran Strand

Explanation: It was bright and green and stretched across the sky. This striking aurora display was captured last month just outside of Östersund, Sweden. Six photographic fields were merged to create the featured panorama spanning almost 180 degrees. Particularly striking aspects of this aurora include its sweeping arc-like shape and its stark definition. Lake Storsjön is seen in the foreground, while several familiar constellations and the star Polaris are visible through the aurora, far in the background. Coincidently, the aurora appears to avoid the Moon visible on the lower left. The aurora appeared a day after a large hole opened in the Sun's corona allowing particularly energetic particles to flow out into the Solar System. The green color of the aurora is caused by oxygen atoms recombining with ambient electrons high in the Earth's atmosphere."

Noctilucent Clouds and Aurora Borealis

Published on Aug 11, 2013 "Displays of Noctilucent Clouds and Aurora during one night are rare. Noctilucent Clouds, NLC's for short, (aka Night Shining Clouds or Polar Mesospheric Clouds) are the world's highest types of cloud forming on the edge of space at height of about 80 km (50 miles) which is also height where auroras occur. Unlike most of other clouds types, which are mostly made of water vapour, NLCs are comprised of extremely small ice crystals. They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon while the lower layers of the atmosphere are in the Earth's shadow. They can be observed in the summer months at latitudes between 50° and 70° north and south of the equator."