Brilliant splashes of color lit up the night skies across North America on May 14-15th during an intense geomagnetic storm, as seen in these photos taken by Mark Urwiller outside Kearney, Nebraska and by Jesús Orjeda in St. Francis, Wisconsin. The display was triggered by a solar coronal mass ejection (CME) hitting Earth’s magnetic field.Auroras form when a “solar wind” of charged particles from the Sun enters Earth’s magnetic field, accelerating electrically charged particles trapped within. The high-speed particles then crash into Earth’s upper atmosphere over the polar regions, causing the atmosphere to emit a ghostly, multicolored glow.[more on aurora borealis on NASA's site]