November 08, 2006
When fast-moving charged particles (electrons and protons) from the Sun reach Earth, they flow down into the Ionosphere along magnetic field lines around both poles. At an altitude of between 60 and 600 miles (100 to 1,000 km), these particles strike atoms and molecules in the upper atmosphere, giving them additional energy that they soon shed in the form of photons. We see this light as the Aurorae Borealis in the Northern Hemisphere and the Aurorae Australis in the Southern Hemisphere.
This photo showing an all-green aurora (caused by the excitation of Oxygen atoms) was taken from Hveragerdi, South Iceland at 01:15 (Greenwich Mean Time) on September 4, 2006. Iceland is located within the Auroral Zone -- a region of 1,600 miles (2,500 km) radius centered on the geomagnetic pole.
A tripod-mounted Canon EOS 300D and 28 mm lens was used. Exposure was 10 seconds at f/4.5 and an equivalent film speed of ISO-800.