How Hot Is The Sun?

The sun is the hottest object in our solar system with an average surface temperature of 10,000 degrees Fahrenheit (5,500 degrees Celsius). However, the actual temperature of the sun varies depending on the different layers of the sun. How hot is each layer of the sun?

The Core

Solar eruptions
Image showing multiple eruptions on the solar surface. Image credit: NASA/SDO

The innermost layer of the sun is its core. Here, temperatures and pressures are at their highest. Temperatures in the sun’s core average at a staggering 27-million degrees Fahrenheit (15-million degrees Celsius). It is here that temperatures and pressures are so high that hydrogen nuclei fuse together to form helium through the process of nuclear fusion. Nuclear fusion in the sun’s core generates a tremendous amount of energy that flows outwards, counteracting the sun’s gravity and allowing it to shine for many billions of years. 

The Radiative Zone

Solar flares
Image showing a solar flare erupting off the solar surface. Image credit: NASA/SDO

Outside the sun’s core is the radiative zone. The radiative zone can be further divided into its outer regions and inner regions. In the inner region of the radiative zone, closest to the core, temperatures average at 12-million degrees Fahrenheit (7-million degrees Celsius). Meanwhile, temperatures in the outer radiative zone average at four million degrees Fahrenheit (two million degrees Celsius). 

The Convection Zone And Surface

Solar surface
The most detailed image ever taken of the sun's surface. Image credit: NASA

Just outside the radiative zone is the convection zone. It is here that heat is transferred to the surface through convection. Temperatures in the convection zone are similar to those in the outer radiative zone, averaging at four-million degrees Fahrenheit (two-million degrees Celsius). Above the convection zone is the surface of the sun, where temperatures average at 10,000 degrees Fahrenheit (5,500 degrees Celsius).

Solar Atmosphere

Corona
Image of the sun showing eruptions from the solar corona. Image credit: NASA/ESA

The sun’s atmosphere is rather strange when it comes to temperature. The photosphere is the layer closest to the surface, and temperatures here are nearly identical to those on the solar surface. Above the photosphere is the chromosphere, and although it is further away from the surface, temperatures here are actually somewhat higher, averaging at around 11,000 degrees Fahrenheit (6,000 degrees Celsius). Beyond the chromosphere is the sun’s corona. It is here where temperatures get weird. Despite the corona being the outermost layer of the sun, temperatures average at around two-million degrees Fahrenheit (one-million degrees Celsius), which is significantly hotter than the other atmospheric layers and the surface. Why the corona is so hot remains one of the biggest mysteries of the sun. 

Solar Temperature 

Layer Temperature

Core

27-million degrees Fahrenheit 

Radiative Zone

12-million to 4-million degrees Fahrenheit 

Convection Zone

4-million degrees Fahrenheit 

Surface

10,000 degrees Fahrenheit 

Photosphere 

10,000 degrees Fahrenheit 

Chromosphere 

11,000 degrees Fahrenheit 

Corona

2-million degrees Fahrenheit 

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