What is the surface temperature of the Sun?

The Sun’s visible surface temperature is approximately 5,500 °C. This visible layer is called the photosphere, and it is the region from which most of the sunlight we see escapes into space.

The Sun does not have a solid surface like Earth. The photosphere is a comparatively thin layer of plasma marking the boundary where the Sun becomes opaque to visible light. Its temperature is about 5,500 °C, or roughly 5,800 kelvins, though measurements vary slightly depending on the reference used.

The temperature changes dramatically inside and outside the photosphere. The Sun’s core reaches roughly 15 million °C, where nuclear fusion occurs. Above the visible surface, the corona can reach millions of degrees, creating the famous coronal-heating puzzle because it is much hotter than the layers immediately below it. Thus, 5,500 °C refers to the Sun’s visible surface—not its core or entire atmosphere.