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Aurora seen from the International Space Station
Astronaut Don Pettit, Expedition Six ISS science officer, took this picture of Earth through a window in the Destiny laboratory on the International Space Station (ISS) on March 24, 2003. "Lately we've been having some extraordinary auroras," he reports. "They meander like big green amoebas crawling across the sky. Sometimes there is a faint touch of red layered above the green. These lights are constantly changing. They swirl. Bright spots come and go. Green blobs transform into upward-directed rays topped by red feathery structures." The picture above shows auroras over Canada with the Manicouagan impact crater in the foreground. Clouds and Earth's surface are illuminated by moonlight. "Here in the same picture we have two interesting space phenomena: asteroid impact damage on the surface of Earth and auroras," notes Pettit.
Auroras are caused by electrons and protons from space raining down on Earth's atmosphere. The solar wind, through a set of complex and fascinating interactions with the Earth's magnetic field, is the ultimate source of energy that drives these particles toward our planet. When they hit the top of the atmosphere, they excite atoms and molecules and make the air glow. Reds and greens come from atomic oxygen, blues from nitrogen. These colorful lights range in altitude from 80 km to 500 km above Earth's surface. The ISS orbits our planet about 400 km high, so the space station can actually fly through auroras. There's no danger to astronauts, though. The aurora-causing electrons and protons are thousands of times less powerful than potentially hazardous cosmic rays.