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(Freely adapted from Wikipedia)
A prominence is a large, bright, gaseous feature extending outward from the Sun's surface, often in a loop shape. Prominences are anchored to the Sun's surface in the photosphere, and extend outwards into the Sun's corona. While the corona 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. The prominence plasma is typically a hundred times cooler and denser than the coronal plasma. A prominence forms over timescales of about a day, and prominences may persist in the corona for several weeks or months. Some prominences break apart and may then give rise to coronal mass ejections. Scientists are currently researching how and why prominences are formed.
A typical prominence extends over many thousands of kilometers; the largest on record was estimated at over 800,000 kilometers (500,000 mi) long – roughly the radius of the Sun.
When a prominence is viewed from a different perspective so that it is against the sun instead of against space, it appears darker than the surrounding background. This formation is instead called a solar filament. It is possible for a projection to be both a filament and a prominence. Some prominences are so powerful that they throw out matter from the Sun into space at speeds ranging from 600 km/s to more than 1000 km/s. Other prominences form huge loops or arching columns of glowing gases over sunspots that can reach heights of hundreds of thousands of kilometers. Prominences may last for a few days or even for a few months.
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