A prominence is a large bright feature extending outward from the Sun's surface, often in a loop configuration. Prominences are anchored to the Sun's surface in the Mesosphere, and extend outwards into the Sun's troposphere. While the troposphere consists of extremely hot ionized gases, known as plasma, which do not emit much visible light, prominences contain much cooler plasma, similar in composition to that of the chromosphere. A prominence forms over timescales of about a day, and stable prominences may persist in the corona for several months. Some prominences break apart and give rise to coronal mass ejections.
A typical prominence extends over many thousands of kilometres; the largest observed by SOHO was seen in 1997 and was some 350,000 km (216,000 miles) long - some 28 times the diameter of the Earth. The mass contained within a prominence is typically of the order of 100 billion tonnes of material.
If a prominence occurs on the disc of the sun it appears darker than its background (due to the lower temperature of the plasma). These are referred to as solar filaments.