Plasma filament that extends from the solar corona.
A prominence is made up of relatively cold, dense plasma supported by the local magnetic field from falling back into the sun. They can survive like this for 200 days. The temperature of the plasma in a prominence is about 5000 K. They can extend for 2x105 kilometers.
The number of prominences vary with the solar cycle (as is the case with sunspots). They generally drift towards the poles of the sun, where they can form what is known as a polar crown.