Quick answer · Updated May 2026
How hot is the Sun?
The Sun's visible surface, the photosphere, is about 5,778 K (5,505 °C). The core, where nuclear fusion happens, reaches roughly 15 million K. The corona — the wispy outer atmosphere — paradoxically reaches over 1 million K despite being far from the core. The exact mechanism for heating the corona to such extreme temperatures remains one of the biggest open questions in solar physics.
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- The Sun's photosphere temperature corresponds to a yellow-white colour — exactly what we see.
- The corona's temperature paradox is being studied by NASA's Parker Solar Probe, which has flown through the corona at over 200 km/s.
- Sunspots are cooler regions, around 3,500 K — that's why they look dark in contrast.
- Over the next 5 billion years the Sun will gradually grow hotter and brighter as it ages on the main sequence.
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