<P> The core of the Sun extends from the center to about 20 -- 25 % of the solar radius . It has a density of up to 7005150000000000000 ♠ 150 g / cm ( about 150 times the density of water ) and a temperature of close to 15.7 million kelvins ( K ) . By contrast , the Sun 's surface temperature is approximately 5,800 K. Recent analysis of SOHO mission data favors a faster rotation rate in the core than in the radiative zone above . Through most of the Sun 's life , energy has been produced by nuclear fusion in the core region through a series of steps called the p -- p ( proton -- proton ) chain ; this process converts hydrogen into helium . Only 0.8 % of the energy generated in the Sun comes from the CNO cycle , though this proportion is expected to increase as the Sun becomes older . </P>
the core of the sun in which the sun 's thermonuclear energy is produced takes up about
extends from the center to about 20 -- 25 % of the solar radius