The coolest of the Sun's several layers is the photosphere, which is the outermost visible layer, according to Astronomy Know How. Temperatures in this layer are usually around 5,780 degrees Kelvin.
The various layers of the Sun average a wide range of temperatures. According to Astronomy Know How, temperatures in the Sun's core rise as high as 15 million degrees. Paradoxically, while the photosphere is the outermost visible layer and burns hot enough to emit visible light, it lies between still hotter layers above and below it. Above the photosphere lie both the chromosphere, which rises to as much as 20,000 degrees Kelvin, and the corona, which has temperatures of up to 3 million degrees Kelvin.