NASA astronaut Scott Kelly shared this photograph on social media, taken from the International Space Station on August 15, 2015. Kelly wrote, "#Aurora trailing a colorful veil over Earth this morning. Good morning from @space_station! #YearInSpace" The dancing lights of the aurora provide spectacular views, but also capture the imagination of scientists who study incoming energy and particles from the sun. Aurora are one effect of such energetic particles, which can speed out from the sun both in a steady stream called the solar wind and due to giant eruptions known as coronal mass ejections or CMEs. After a trip toward Earth that can last two to three days, the solar particles and magnetic fields cause the release of particles already trapped near Earth, which in turn trigger reactions in the upper atmosphere in which oxygen and nitrogen molecules release photons of light. The result: the Northern and Southern lights.