What is the core temperature of the Sun, in millions of Kelvin?

The core temperature of the Sun is about 15.7 million kelvin. At this extreme temperature and pressure, hydrogen nuclei move rapidly enough for nuclear fusion to occur in the Sun’s central region.

The Sun’s core extends from its center to roughly be one-quarter of the solar radius. Its immense gravity compresses the plasma, raising the density and pressure to levels that allow the proton–proton chain to convert hydrogen into helium. A small amount of mass is transformed into energy, which ultimately emerges as sunlight and other radiation.

The energy does not travel straight from the core to space. Photons repeatedly scatter through the surrounding radiative zone, a journey that can take a very long time. Farther out, convection carries hot plasma upward and cooler material downward through the convection zone. The visible surface, or photosphere, is much cooler—about 5,500 kelvin.

A common mix-up is treating the core temperature as the Sun’s surface temperature. Another is assuming the Sun burns like a chemical fire. Its energy comes from nuclear fusion, and the rate is self-regulating: if the core contracts or expands slightly, temperature and fusion rates change, helping maintain balance over immense timescales.