CLAUS LUNAU / SCIENCE PHOTO LIBRARY CLAUS LUNAU / SCIENCE PHOTO LIBRARY
Earth's magnetic field and aurora. Illustration of charged particles (yellow) impacting the magnetic field (blue lines) surrounding the Earth, producing an auroral discharge (yellow, upper right). Some of the particles are repelled by the magnetic field. The Earth's magnetic field, generated by eddies set up in the planet's liquid core, extends outwards into space for tens of thousands of kilometres, protecting the planet from high-energy radiation from the Sun. An aurora occurs when charged and energetic particles from the Sun (the solar wind) are drawn by Earth's magnetic field to the polar regions. Hundreds of kilometres up, they collide with gas molecules and atoms, causing them to emit light.
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