What causes the colours of the aurora?

Infographic on the colours of the aurora. Auroras result from charged particles from the sun hitting the Earth’s magnetic field. The particles follow Earth’s magnetic field lines and enter Earth’s atmosphere at the poles where the magnetic field is at its weakest. When they enter the atmosphere, the charged particles collide with atoms and molecules in the air. The collision results in the excitation of atoms and molecules, which give off varying colours of light as they lose the additional energy. The different colours of the aurora are caused by the collision of charged particles, usually electrons, with different gases at varying altitudes in the atmosphere. Red is rare and caused by oxygen atoms high in the atmosphere, green is caused by oxygen atoms lower down, and blues and purples originate from molecular nitrogen.
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A magical fox, running across the Arctic fells, its tail spraying snow and sparks into the air. The dead, playing football in the heavens with a walrus skull. Or the souls of dead children, dancing in the sky.

These are myths surrounding the aurora, stories ancient cultures close to the North Pole told to explain the ethereal lights they saw flickering in the night sky above their heads. Now, we know that these breathtaking displays aren’t of supernatural origin but due to chemical processes high in the atmosphere. This graphic explains how auroras form and what causes the different colours.

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What materials are strong enough for a space elevator? – in C&EN

Promo image for this infographic. The full infographic with alt-text is available on the C&EN site.
Click to view the full graphic on the C&EN site

Space elevators, a way of getting cargo and materials into space without rockets, have made frequent appearances in science fiction for decades. Making them a reality, however, is challenging. In this latest edition of Periodic Graphics in C&EN, we take a look some of the material requirements for space elevators, and which existing materials might be close to meeting these requirements. See the full graphic on the C&EN site.

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