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October 2003

The Aurora Borealis

The Aurora Borealis (or Northern Lights) are a rare but beautiful sight in Iowa. This image, a conventional color-film photograph by Guillermo Gonzalez (just west of Ames), records the colors and structures of a magnificent auroral display in October 2001 that was produced by a "coronal mass ejection" from our Sun.

The aurora is caused by a flood of charged atomic nuclei racing away from disturbances on the Sun. These particles then are captured by the magnetic field of the Earth, and come speeding in to the upper atmosphere. The energy from these particles can cause the gas in the thin upper atmosphere to glow, similar to the way nebulae glow from the energetic light from nearby stars, producing colors that are characteristic of the composition of our atmosphere.

The beautiful, intricate, and rapidly changing colors result from changes in the flow of material from the Sun and the Earth's magnetic field. Our colleagues at the University of Iowa are among the world's leaders in studying such phenomena.