The on-off switch also controls the volume. The components are housed in a small metal box with a whip antenna and powered by a 9-volt battery. I fire up a little unit called a WR-3 that I bought for $60 back in the mid-1990s. Radio waves given off by auroras and other forms of natural 'Earth energy' like lightning range from 19 to 1,800 miles long or longer! To make them available to our senses we use a radio receiver. The pigments in our retinas convert these waves into visible images of the world around us. We're used to waves of light which are very, very short, measuring in the millionths of an inch long. This handheld device converts very low frequency radio waves produced from the interaction of the solar electrons and protons with the Earth's magnetic field into sounds you can listen to with a pair of headphones. If you're like me and hard of auroral hearing, a small VLF radio receiver will do the job nicely. Given that the aurora is never closer to the ground than 50 miles, the air is far too thin to transmit any weak sound waves that might be produced to your ears. It's a psychological thing - you see a spectacular display of auroral light and in your head hear sounds your imagination might expect like crackling and whooshing. Of course another reason people might hear auroras is they imagine a soundtrack.
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