The sun is not uniformly hot — temperature varies enormously between its layers, and in a counterintuitive way.
Temperature by Layer
| Layer | Temperature | Notes |
|---|---|---|
| Core | ~15,000,000°C (27M°F) | Where nuclear fusion occurs |
| Radiative zone | ~7,000,000°C | Energy slowly diffuses outward |
| Convective zone | ~2,000,000°C | Hot plasma bubbles rise to surface |
| Photosphere (surface) | ~5,500°C (9,932°F) | The visible surface we see |
| Chromosphere | ~20,000°C | Just above the surface; seen during eclipses |
| Corona (outer atmosphere) | 1,000,000–3,000,000°C | Paradoxically hotter than the surface |
The Corona Mystery
One of the great unsolved problems in solar physics is why the corona — the sun's outer atmosphere — is dramatically hotter than the surface. Normally, you'd expect temperature to decrease as you move away from a heat source. Scientists believe the answer involves magnetic waves carrying energy from the interior outward, but the exact mechanism remains actively researched.
Nuclear Fusion in the Core
The sun's core converts approximately 600 million tons of hydrogen into helium every second through nuclear fusion. This process converts a small amount of mass into an enormous amount of energy (E = mc²). The energy produced in the core takes thousands to millions of years to travel to the surface before being released as light and heat.