When all its nuclear fuel is exhausted, the star dies, possibly in a supernova explosion. Streamers An extension of rays from the sun's corona. At its center, the Sun has a density over 100 times that of water, a pressure of over 1 billion atmospheres, and a temperature of about 15,000,000 degrees Kelvin. This temperature is high enough for the occurrence of nuclear reactions, which are assumed to be the source of the Sun's energy. An area seen as a dark spot on the photosphere of the Sun.
Sunspots are concentrations of magnetic flux, typically occurring in bipolar clusters or groups.
They appear dark because they are cooler than the surrounding photosphere. Transition Region A layer of the solar atmosphere a few hundred kilometers thick that lies between the chromosphere and the corona, within which temperatures rise from about 10,000 to over one million Kelvin.