What are the layers of the Sun, from core to corona?
The short answer
The Sun has six layers. Working outward: the core, where fusion happens; the radiative zone, where light bounces slowly outward; the convective zone, where hot gas churns; the photosphere, the visible surface; the chromosphere, a thin pink layer; and the corona, the outer atmosphere that stretches millions of kilometres into space.
The core is the only part that makes energy
At 15 million degrees and crushed to a density greater than metal, the core is where hydrogen fuses into helium. Every photon of sunlight that has ever warmed anything began here. It occupies only the innermost portion of the Sun, yet it is responsible for every bit of the star's output. The other five layers do not generate anything. They are the route the energy takes on its way out.
The radiative zone is a traffic jam that lasts millennia
Immediately above the core, the gas is so densely packed that light cannot travel in a straight line. A photon moves a short distance, gets absorbed, is re-emitted in a random direction, and does it again. And again. Crossing this single layer can take thousands of years. It is the slowest part of the journey by an enormous margin, and it is the reason sunlight is far older than it looks.
The convective zone boils like a pot of soup
Further out, the gas thins enough that it can move in bulk rather than just passing energy along. Hot gas rises, reaches the cooler upper region, gives up its heat, and sinks back down, over and over. The cells of rising and falling gas are enormous. A single convection cell can be wider than France. If you look at high-resolution images of the Sun's surface, the grainy texture you see is the tops of these cells.
The photosphere is the surface we actually see
This is where the Sun finally becomes transparent and light escapes into space at around 5,500C. It is also surprisingly thin, a few hundred kilometres against a star nearly 1.4 million kilometres across, which in proportion is roughly the skin on an apple. When you look at the Sun in a photograph, this is the layer you are looking at. Sunspots sit here too.
The chromosphere is thin, pink, and usually invisible
Just above the photosphere sits a thin layer that glows reddish-pink. You almost never see it, because the surface below is overwhelmingly brighter. Jets of gas called spicules rise through it constantly, and they are not small: a single one can be taller than many times the height of Mount Everest stacked up. The chromosphere becomes briefly visible as a red rim during a total solar eclipse.
The corona is a million-degree mystery
The outermost layer stretches millions of kilometres into space and is visible from Earth only during totality, when the Moon covers the bright disc. Here is the part that still puzzles physicists: the surface below is about 5,500C, but the corona above it exceeds a million degrees. Temperature normally falls as you move away from a heat source. The coronal heating problem is a genuine open question in solar physics, not a simplification for a children's programme.
Sources
Full transcript: Layers of the Sun Explained: Core to Corona
A tour of the sun's layers. Last time we visited the sun's engine room: the core, where sunshine is made. And way out here is the bright surface we see from Earth. But wait, what's in between?
A lot, it turns out. The sun is built in layers, like an onion, and today, Watt is giving us the grand tour. Welcome back to Watt and Why! Today, a tour of the sun's layers: six amazing stops from the very middle of the sun all the way out to its crown.
All aboard! Here's the map: deep inside, the core. Wrapped around it, the radiative zone, then the convective zone, then the photosphere—that's the part we actually see— the chromosphere, and stretching way out into space, the corona. Six layers.
Let's visit every single one. Stop one: the core. Hey, you know this place: 15 million degrees, squeezed tight, smashing hydrogen into helium, making every bit of the sun's energy. Every sunbeam that ever warmed your face started right here.
Okay, say bye! We're heading up. Stop two: the radiative zone. It is packed in here.
So crowded that light can't fly straight—it bounces and bounces, a tiny zigzag at a time. Crossing this one layer can take thousands of years. That incredible journey gets its own episode next time. Stop three: the convective zone.
And suddenly, everything is moving. Hot gas rises, cools off, and sinks back down, round and round, like soup bubbling in a pot. And these bubbles are enormous—one single bubble can be bigger than France! Enjoy the ride, Watt!
Stop four: the photosphere. This is the surface, the part our eyes see. And here at last, light breaks free. After all that bouncing and boiling, sunlight escapes into space at a toasty 5,000 degrees.
Fun fact: this layer is surprisingly thin, like the skin on an apple. Stop five: the chromosphere. A thin, shy layer that glows pink. You almost never see it because the bright surface below steals all the attention.
Little jets of gas dance across it like flames, each one taller than a thousand Mount Everests! And stop six: the corona—the sun's crown. It stretches millions of kilometers into space, but sunlight is so bright that you can only see it when the moon slides perfectly in front of the sun—a total eclipse. There it is!
Isn't that beautiful? Now, the corona keeps a secret: the surface below is 5,500 degrees, right? The corona floating above it is over a million degrees! Hotter as you move away from the heat?
That's upside down! And here's the best part: scientists are still figuring out exactly why. A real, live unsolved mystery. Let's ride the whole way back: from the core, through the bouncing, up with the boiling, out at the photosphere, past the pink chromosphere, and through the crown into space.
What a trip! So remember: the sun has six layers from core to corona. Sunlight breaks free at the photosphere, and the corona, the outermost layer, is a million-degree mystery. Next time, we follow one tiny piece of light on the longest escape in the solar system.
See you on Watt and Why!
Transcript of the episode, lightly cleaned for readability.
Sample question
Question 1 of 10
What is the correct order of the Sun's layers, working outward from the centre?
- Core, radiative zone, convective zone, photosphere, chromosphere, corona correct
- Core, corona, photosphere, chromosphere, radiative zone
- Photosphere, core, convective zone, corona
- Corona, chromosphere, core, photosphere
Energy is produced in the core and works its way outward through each layer in turn.
That is one of 10. The rest are not shown here, and the answer order changes every time you take the quiz.
Written by Watt & Why. Published 9 September 2026. Last reviewed 17 October 2026.