Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2010 October 6
Explanation: Are those green clouds or aurora? Photographed above two weeks ago, puffy green aurora help the Moon illuminate the serene Willow Lake and the snowy Wrangell and Saint Elias Mountains in eastern Alaska, USA. Although aurorae might first appear to be moonlit clouds, they only add light to the sky and do not block background stars from view. Called northern lights in the northern hemisphere, aurorae are caused by collisions between charged particles from the magnetosphere and air molecules high in the Earth's atmosphere. If viewed from space, aurorae can be seen to glow in X-ray and ultraviolet light as well. Predictable aurorae likely occur a few days after a powerful magnetic event has been seen on the Sun.
Authors & editors:
Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
A service of: ASD at NASA / GSFC
& Michigan Tech. U.