Aurorae, Norway
Seen by Marius Sollerud 26th Sept '11 at Bysetermåsan, 10 miles SE of Oslo. Olympus E3, 8 mm fisheye-lens. 15 sec, ISO 400, F/3,5
©Marius Sollerud, shown with permission.


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Electrons from Earth�s night-side magnetotail produced this display.   Whilst the particles filling the our magnetosphere are from the sun, they are usually of much too low an energy to produce bright aurorae directly.

Magnetotail electrons are accelerated downwards into Earths polar ovals reaching energies of 1-100KeV. They collision ally excite oxygen and nitrogen in the upper atmosphere. Excited atoms usually lose their energy in collisions but the latter are so infrequent at high altitudes that radiative de-excitation gets a chance to produce auroral light.

The green aurorae are from excited oxygen atoms (O 1S to 1D) 100-150 km high. The red glow is from a different excited state of oxygen atoms (O 1D to ground state 3P) and occurs above 150 km.