How Hot is the Sun?
The Sun is about 10,000 degrees Fahrenheit, or 5,600 degrees Celsius. The center of the Sun is its hottest point, at about 27,000,000 degrees Fahrenheit, or 15,000,000 degrees Celsius.
The temperature of the Sun is hottest in the center, and gradually gets lower as you reach the surface. However, the temperature of the Sun rises again from the surface outward to its atmosphere.
The Solar Atmosphere is the Sun’s uppermost layer, called the Corona. This feature can be seen as a bright halo of light surrounding the Sun during a solar eclipse. The Corona of the Sun can reach millions of degrees.
A solar prominence at the edge of the Sun. Photo credit: Trevor Jones
The high temperatures found in the Corona are still a mystery to scientists. Even though the Sun’s atmosphere is far from its surface (the Corona starts around 10,000 km above the solar photosphere), it is hundreds of times hotter than the surface of the Sun.
The NASA IRIS mission found ‘packets’ of hot material that travel from the surface of the Sun to the Corona, where these heat packets explode and release energy as heat.
The coolest parts of the Sun are the dark areas of magnetic disturbances erupting on the photosphere, also known as sunspots. Sunspots are usually about 6,700 degrees Fahrenheit.
A visual representation of each layer of the Sun. The European Space Agency.
Temperature by Solar Layer
Understanding the Sun’s temperature means looking beneath its glowing surface. Each layer of the Sun, from the dense, fusion-powered core to the wispy outer corona, has its own temperature range and unique behavior.
Here’s how the heat changes as we move outward through the solar structure:
| Solar Layer | Approx. Temperature (°C) | Description |
|---|---|---|
| Core | ≈ 15,000,000 °C | The nuclear furnace at the heart of the Sun. Hydrogen atoms fuse into helium here, releasing enormous energy that drives all solar activity. |
| Radiative Zone | 2,000,000 – 7,000,000 °C | Energy from the core moves slowly outward as photons are absorbed and re-emitted countless times — taking thousands of years to escape. |
| Convective Zone | ~2,000,000 °C near bottom → ~5,500 °C at top | Hot plasma rises and cool plasma sinks in large convection cells, similar to boiling water. This churning motion creates the Sun’s granulated surface texture. |
| Photosphere | ≈ 5,500 °C (9,932 °F) | The visible “surface” of the Sun that we see in white light. Sunspots appear darker because they are cooler (around 3,800 °C). |
| Chromosphere | ≈ 20,000 °C | A thin reddish layer seen during solar eclipses. Temperatures rise again here due to magnetic activity. |
| Corona | 1,000,000 – 3,000,000 °C (and higher during flares) | The Sun’s outer atmosphere extends millions of kilometers into space. Despite its low density, it’s far hotter than the surface — a mystery still being studied by solar physicists. |
Key Takeaway: The Sun’s temperature doesn’t simply drop as you move away from the core — it dips at the surface, then spikes again in the outer atmosphere. This unusual temperature profile is one of the Sun’s most fascinating mysteries.
Quick Visual Summary
- Hottest region: Core — where nuclear fusion occurs
- Coolest region: Photosphere — the visible “surface”
- Hot outer layer: Corona — heated by magnetic and wave interactions
As a full-time astrophotographer, I regularly document solar activity using a specialized solar telescope. Here is a look at the Sun’s surface in detail using a hydrogen-alpha telescope (Sky-Watcher Heliostar 76 Hα).
Why Is the Corona Hotter Than the Surface?
One of the biggest mysteries in solar physics is why the Sun’s outer atmosphere, the corona, is millions of degrees hotter than its visible surface (the photosphere). You’d expect temperatures to drop the farther you move from the Sun’s core, yet the corona defies that logic.
The Sun’s surface averages about 5,500 °C, but its corona can exceed 1–3 million °C (nearly 500 times hotter). For decades, scientists have tried to understand how energy travels from the relatively cool photosphere to the intensely hot corona. Since the corona is much thinner than the layers below it, it can’t simply be heated by direct contact. Instead, researchers believe magnetic energy and wave motion are key.
Spacecraft like NASA’s Parker Solar Probe and ESA’s Solar Orbiter are helping solve this puzzle by flying closer to the Sun than ever before. Their measurements of solar wind, magnetic fields, and charged particles are revealing how energy moves through the Sun’s upper atmosphere.
Leading Theories
- Magnetic Reconnection: The Sun’s magnetic field lines constantly twist, tangle, and snap. When they reconnect, they release bursts of energy that rapidly heat nearby plasma — similar to miniature solar flares.
- Wave Heating (Alfvén Waves): Vibrations within magnetic field lines can carry energy upward from the lower layers. When these waves dissipate in the corona, they deposit heat directly into the plasma.
- Nanoflares: Countless tiny, almost undetectable bursts of energy may occur throughout the corona, collectively maintaining its extreme temperature.
What is the Sun made of?
The Sun is composed of hydrogen and helium (about 92% hydrogen and 8% helium). It also contains small amounts of other elements, such as carbon, oxygen, nitrogen, magnesium, and iron.
Nuclear fusion takes place in the Sun’s core, where it burns millions of tons of hydrogen a second. This process creates incredible amounts of energy, including the heat and light of the Sun.
Nuclear fusion turns hydrogen into helium at the Sun’s core. NASA.
The Sun’s surface is covered in intense magnetic fields. These magnetic fields affect the charged particles in the Sun’s corona, forming helmet streamers, coronal loops, and polar plumes.
Eventually (about 5 billion years from now), the Sun’s hydrogen fuel will run out. When this occurs, the Sun will begin to die.
Solar Flares and Sunspots
Solar Flares are localized, intense eruptions of electromagnetic radiation that occur in the Sun’s atmosphere. A solar flare occurs in an active region of the Sun that may include coronal mass ejections (CMEs).
This solar phenomenon is believed to take place when the magnetic energy in the Sun’s atmosphere accelerates charged particles in the surrounding plasma. The result is an electromagnetic radiation emission event.
Sunspots are dark regions of strong magnetic fields on the Sun. They can trigger eruptions such as CMEs. These regions appear darker because they are much cooler than the surrounding photosphere.
Observing and Photographing Sunspots on the Sun
If you own a pair of certified solar filter glasses (like the ones used for a solar eclipse), you can safely look at the sun’s surface to see if there are any sunspots.
One of the easiest ways to photograph sunspots is to use your smartphone, with a certified solar filter in front of the camera lens. This is the same procedure many people use to photograph a total solar eclipse with their phone.
Even better, you can use a beginner-friendly smart telescope like the SeeStar S50 or DWARF 3 (both include dedicated white-light solar filters) to take impressive images of the sun’s surface.
I photographed the Sun with a certified white-light filter and a smart telescope. Notice the sunspots across the Sun’s disc.