Solar Filament, October 15, 2010. This photograph was taken with a hydrogen alpha scope that only shows one wavelength of light, at 656.3 nanometres. This is the particular wavelength of hydrogen alpha light. Observing the Sun in hydrogen alpha makes it possible to see structural details.
The dark streak across the centre of this photograph is a solar filament. A filament has the same structure as a solar prominence, but when it is seen against the background of the Sun (instead of on the edge) it has a thread-like appearance. This huge cloud of Hydrogen plasma was held aloft above the Sun's surface by powerful magnetic fields. The estimated length of this particular solar filament was 400,000 km long more than the distance between the Earth and the Moon.
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