Aurora Observed from Space Station
January 16, 2004
According to Expedition 6 Science Officer Don Pettit, aboard the International Space Station (ISS), being in orbit around the Earth offers a unique perspective on auroras. He mentioned that when their orbit coincided with local midnight at high latitudes, the lights were turned down so that it was possible to peer out the windows at the breathtaking views of the shimmering northern lights. The above photo was taken from the ISS as it orbited over the Southern Hemisphere, approximately 400 km above the Earth’s surface, on April 20, 2003.
Most of the auroral light is emitted by oxygen atoms excited from bombardment by charged solar particles. Charged particles consisting of atomic fragments released by the Sun stream through space and run into Earth’s magnetic field. When a charged particle encounters our magnetic field, a force perpendicular to the motion is created, which diverts the particle into a spiral path until it collides with atoms in the upper atmosphere. The collisions excite the atoms (oxygen and nitrogen) into emitting light, in much the same way that electrons pumped inside of a glass tube filled with neon gas create a neon light. Green light is the color most commonly observed. It's emitted from excited oxygen, centered around a wavelength in the electromagnetic spectrum of 558 nanometers. Red light, emitted about wavelengths in the 630 nanometer region, is less infrequently observed. Green emissions extend from about 100 km altitude to approximately 300 km, whereas the red emissions lie on top of the green and extend to perhaps 500 km.