From Wikipedia:
“A prominence is a large, bright 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. 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.”
Reference: en.wikipedia.org/wiki/Solar_prominence

You can observe a nice comparison between the size of the earth to that of the solar prominence at http://www.astronomycamerasblog.com/2009/11/27/solar-prominence/
Taken in Varanasi, India.