On some nights the sky is the most interesting show in town. This picture captures a particularly active and colorful display of aurora that occurred recently high above Alaska. Auroras are more commonly seen by observers located near the Earth's poles. Aurora light results from solar electrons and protons striking molecules high in the Earth's atmosphere. Planetary aurora activity can sometimes be predicted after particularly active solar coronal mass ejections.
Auroras are caused by high-energy particles from the solar wind that are trapped in the Earth's magnetic field. As these particles spiral back and forth along the magnetic field lines, they come down into the atmosphere near the north and south magnetic poles where the magnetic field lines disappear into the body of the Earth. The delicate colors are caused by energetic electrons colliding with oxygen and nitrogen molecules in the atmosphere. This excites the molecules, and when they decay from the excited states they emit the light that we see in the aurora.
Click on the image for more information about Auroras and more great pictures.