Northern Lights LakeRibbons of green auroras are reflected in Northern Light Lake (map), north of Grand Marais, Minnesota, on September 9.Such auroral displays are triggered when clouds of charged particles from the sun—known as coronal mass ejections (CMEs)—slam into Earth's magnetic field. As the particles get funneled along field lines toward the Poles, they collide with molecules in Earth's atmosphere, infusing them with extra energy. The molecules in turn release the energy as light. (Also see pictures: "Multicolored Auroras Sparked by Double Sun Blast.")On September 5 to 7 the sun sent out a series of CMEs associated with several powerful solar flares. The first particle cloud reached Earth a few days later, triggering 18 hours of auroras that were seen in the United States as far south as Maine, Michigan, Vermont, and Washington State.Photographer Bryan Hansel used a fisheye lens to capture the extent of the glow over Northern Light Lake: "The full moon was out, and I was worried that the colors would wash out. There was also a fog building on the lake, which would later obscure the display," Hansel said in an email."But during this picture the northern lights intensified and were overhead and the fog stayed away. ... The light from the full moon lit up the lake. I had a couple of friends with me, and they were clapping and cheering when I took this photo."

Photograph by Bryan Hansel