A filament-like protuberance from the chromosphere of the sun. Prominences can be observed visually (optically) whenever the sun's disk is masked, as during an eclipse or by using a coronagraph; and can be observed instrumentally by filtering in certain wavelengths, as with a spectroheliograph. A typical prominence is 6000 to 12 000 km thick, 60 000 km high, and 200 000 km long. These features appear as filaments when they are seen against the solar disk.