How Hot Is the Sun?

The sun, a massive nuclear-powered source of energy at the center of the solar system, generates the heat and light that sustain life on Earth. But how hot is the sun?

The answer is different for each part of the sun. Arranged in layers, the sun varies in temperature: It is hottest at its center, and cooler in its outer layers — until it strangely reheats at the fringes of the sun's atmosphere.

At the sun's core, gravity causes intense pressure, and temperatures of up to 27 million degrees Fahrenheit (15 million degrees Celsius). This generates the nuclear fusion responsible for the star's energy.

That energy then radiates outward in the sun's inner radiative zone, which lacks the heat and pressure to cause fusion. In that zone, temperatures drop from 12.6 million to 3.6 million F (7 million to 2 million C). In the next zone, called the convective zone, plasma bubbles carry heat to the surface. This zone hits about 3.6 million F.

Next, energy reaches the surface of the sun, or photosphere, producing the light visible from Earth, and a comparatively chilly 10,000 F (5,500 C ).

For unknown reasons, however, temperatures rise again in the sun's atmosphere, hitting up to 3.6 million F in the star's outermost corona.

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