<P> The core of the Sun is considered to extend from the center to about 0.2 to 0.25 of solar radius . It is the hottest part of the Sun and of the Solar System . It has a density of 150 g / cm ( 150 times the density of liquid water ) at the center , and a temperature of 15 million kelvins ( 15 million degrees Celsius , 27 million degrees Fahrenheit ) . The core is made of hot , dense plasma ( ions and electrons ) , at a pressure estimated at 265 billion bar ( 3.84 trillion psi or 26.5 peta pascals ( PPa ) ) at the center . Due to fusion , the composition of the solar plasma drops from 68 - 70 % hydrogen by mass at the outer core , to 33 % hydrogen at the core / Sun center . </P>
what is the approximate temperature at the center of the sun where nuclear fusion occurs
15 million kelvins ( 15 million degrees Celsius , 27 million degrees Fahrenheit ) .