Dark elongated features, seen in H-alpha, are known as filaments. They appear as bright prominences, when seen projected above the solar limb. These are relatively dense and cooler clouds of material supported by the magnetic fields in the solar corona. Filaments may persist on the solar surface for very long durations, up to several solar-rotations, in those regions where magnetic field variations are slow. These are known as 'quiescent filaments'. However, filaments within or close to active regions may show dramatic activities in much shorter time periods.