The aurora borealis seen high in the Earth?s ionosphere (credit: NASA)

The aurora borealis seen high in the Earth?s ionosphere (credit: NASA)

Ionosphere / Atmosphere

An altitude of 100 km is usually thought of as the boundary where our Earth ends and the emptiness of outer space begins. In fact the atmosphere extends much farther than that, into a region called the ‘ionosphere’. A vanishingly thin scattering of oxygen atoms reaches to a few hundred kilometres, blending into an even thinner scattering of hydrogen atoms yet further beyond. Exposed to the full ultraviolet glare of the Sun, the electrons are stripped away from these atmospheric gases to produce plasma – an electrically conductive 'soup' of positively and negatively charged particles (ions and free-flying electrons). These insubstantial layers of gas and plasma are the interface between the Sun’s electromagnetic energies and our planet’s environment. The beguiling ‘Northern Lights’ (and their Southern counterparts) are the beautiful side effects of the electromagnetic link to our Sun.

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The aurora over the Firth of Clyde (credit: David Palmar Photography www.photoscot.co.uk)

Aurora alert!

According to a popular internet search engine, the phrase ?aurora borealis? was among the top one hundred searched-for terms in the UK in 2005. The aurora really has to be seen to be appreciated. Neit...

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Man-made aurora viewed through an image-intensifying camera.  In this view, looking up from the ground, the red patch of aurora is only visible when the transmitter is turned on (credit: Mike Kosch, Lancaster University).

Man-made aurorae

Human space exploration and satellite survival are compromised by the variable radiation levels encountered in near-earth space. Given our society?s ever-increasing reliance on satellite systems, ther...

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Imaging the Earth?s ionosphere (credit: Cathryn Mitchell, University of Bath)

3D 'movies' of the ionosphere

A conventional hospital X-ray photograph is a 2-dimensional shadow of a 3-dimensional subject. If one bone lies in front of another, that second bone might not show up on the photo. ?Tomography? overc...

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