The temperature at the sun's surface is approximately 10,000 degrees Fahrenheit. Moving towards the core of the sun, the temperature increases significantly to about 27,000,000 degrees Fahrenheit. Pressure at the core is also extremely high.
Nuclear fission occurs in the sun's core, where the compression of hydrogen atoms produces helium. Large amounts of energy are created during this process, which radiates outwards towards the surface and beyond.
The sun's heat generates from the solar surface outwards towards a section of the solar atmosphere called the corona. The temperature in the corona can reach as high as 3.5 million degrees Fahrenheit. The corona is the topmost layer of the solar atmosphere, which is visible as a halo during a total solar eclipse.