A cloud-like feature, visible especially in Ηα‎ light, located in the Sun’s corona but cooler and denser than the corona. Prominences have temperatures of around 10 000 K, typical of the solar chromosphere, and densities 100 times higher than the corona. They are often seen around the Sun’s limb at total solar eclipses. In Ηα‎ light they can be seen silhouetted against the Sun’s disk, when they are termed filaments. They are categorized as quiescent prominences or active prominences, according to their behaviour. Active-region prominences have rapid motions and last for only a few days, whereas quiescent prominences can last for at least a month (one solar rotation). Between the relatively cool prominence material and the hot corona is a transition region or sheath in which temperatures range from 15 000 to 60 000 K. Prominences form along magnetic inversion lines and are thought to be supported by magnetic fields. They are most frequent during the rising part of the solar cycle.

http://sohowww.nascom.nasa.gov/pickoftheweek/old/03sep2010/