plage regions and active regions. Quiescent prominences, or quiescent filaments, form in the weak background magnetic field far from any active regions. Unlike active region prominences, quiescent prominences are relatively stable and can have lifetimes ranging from weeks to months, hence the name . Quiescent prominences are typically located at high latitudes around what is referred to as the polar crown. Additionally, quiescent prominences generally reach much greater heights in the corona than active region prominences. Active region and quiescent prominences can also be differentiated by their emitted spectra. The spectra of active region prominences is identical to that of the upper chromosphere having strong He II lines but very weak ionized metal lines. On the other hand, the spectra of quiescent prominences is identical to the spectra measured at in the chromosphere with strong H, He I, and ionized metal lines, but weak He II lines. Morphology Filament channels Prominences form in magnetic structures known as filament channels where they are thermally shielded from the surrounding corona and supported against gravity. These channels are found in the chromosphere and lower corona above divisions between regions of opposite photospheric magnetic polarity known as polarity inversion lines (PIL). The presence of a filament channel is a necessary condition for the formation of a prominence, but a filament channel can exist without containing a prominence. Multiple prominences may form and erupt from within one filament channel over the channel's lifetime. The magnetic field making up the filament channel is predominantly horizontal, pointing in the same direction on both sides of the PIL (see ). Prominence material does not occupy the entire width of the filament channel; a tunnel-like region less density than the corona, known as a coronal cavity, occupies the volume between the prominence and the overlying magnetic arcade. Spines and barbs Typical prominences have a narrow structure oriented along the filament channel known as a spine. The spine defines the upper main body of a prominence and is generally in the form of a vertical sheet that diverges towards the photosphere at both ends. Many prominences also have smaller structures referred to as barbs that similarly diverge from the spine towards the chromosphere and photosphere. Spines and barbs are both composed of thin threads that trace the magnetic field similar to chromospheric fibrils. The cool prominence material that makes up spines and barbs—the prominence core—is surrounded by a prominence-corona transition