The haunting glow of the aurora arises when energized electrons and ions excite gases in the atmosphere. Beams of radio waves can induce auroralike light, but emissions have been too faint to detect with the naked eye. Trying to make the best use of instrument time, Todd R. Pedersen of Hanscom Air Force Base in Massachusetts and Elizabeth A. Gerken of Cornell University trained their radio antennas on a natural aurora event in Alaska. They aimed for a lower than usual region of the atmosphere, about 100 kilometers high, where ions dissipate quickly compared with higher altitudes. For a few minutes last March small green speckles appeared amid the background glow—bright enough in principle to see directly, as the researchers describe in the February 3 Nature. If the effect proves reproducible, Pedersen says, the technique could serve as a tool for atmospheric studies.
This article was originally published with the title "Aurora Born of Radio" in Scientific American 292, 4, 32 (April 2005)