The International Telecommunication Union designates ELF waves as those with frequencies from 3 to 30 Hz. Their wavelengths stretch from 10,000 to 100,000 km. Humans have used them for submarine communication, but because it's difficult to build an antenna long enough to produce the waves, few man-made systems deal with them. They are also generated naturally by lightning and the planet's magnetic field, and may have been identified on Saturn's moon Titan.
ELF Radio Waves Stretch Farther Than The Earth Is Wide
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Key Facts In This Video
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Visible light is the only set of electromagnetic radiation that propagates in water. 01:52
Any particle that has no mass travels at c, the speed of light, without acceleration. 03:22