Quiescent prominences occur as long-lasting cool sheets of matter in the surrounding hot corona at the base of coronal streamers. Seen on the disk they appear as dark filaments dividing regions of opposite magnetic polarity.
In this paper a theoretical model is presented, which describes the general appearance of quiescent prominences.
It is shown that the neutral sheet between two regions of oppositely directed magnetic fields is thermally unstable. This gives rise to compression and cooling of coronal material to prominence material in a characteristic time of the order of one day for a field strength of 0.5 gauss in the lower corona.
It is assumed that due to the finite electrical resistivity of the plasma, filamentary structures are formed by the 'tearing-mode' resistive plasma instability. These structures are thermally insulated from the hot surroundings by the newly formed closed azimuthal magnetic field configuration.
It has been shown that for fine structures with a diameter of 300 km the growth rate of the 'tearingmode' instability is of the same order as the cooling time. The occurrence of fine structures within the prominence is of vital importance for their origin.