Layers of the Sun Explained: Exploring Our Home Star

 Our Sun is a beautifully complex star. Keeping itself alive via nuclear fuel, the Sun is a vast system of layers and fascinating processes. But, while complex, understanding the Sun in general is simple and exciting! Let’s dive in and examine all the layers of the Sun.

 

Layers of the Sun Explained – Interior

First, let’s dive deep and explore the interior of the Sun. Three layers, a core, radiative zone and convective zone comprise the insides of our star.

Core

Layers of the Sun Explained Core

Deep within the Sun’s interior lies the core. Initially, all the power, energy and heat generated by the Sun is born here. In other words, the core is the Sun’s heart.

Sun Solar Flare Picture

Real photo of energy bursting from inside of the Sun in a violent solar flare
Photo: NASA/SDO

Pressures and temperatures are at their highest levels within the core. In fact, temperature at the core can reach a staggering 27 million degrees! Under such extreme conditions, atoms move so quickly and are squeezed so tightly that their nuclei are smashed together. But, instead of destroying each other, the two atoms combine to form heavier, more complex atoms. In the case of our Sun, hydrogen is constantly fused into helium. This process, called nuclear fusion, is the lifeblood fuel of all stars.

Finally, as the atoms combine, they release excess energy to remain stable. In the end, this excess energy will become the light and heat we experience here on Earth.

Due to the massive size of our Sun, it creates tremendous gravity, constantly pushing inward on itself. However, the core’s powerful nuclear fusion is constantly pushing outward. Ultimately, the Sun stays alive in this delicate balance of inward gravity and outward nuclear energy.

Radiative Zone

Layers of the Sun Explained Radiative Zone

 

Next, beyond the core lies the radiative zone. At this point, density, pressure and temperature gradually decrease.

Now, the energy created from the core’s nuclear fusion is carried through the radiative zone. At this point, the energy is now in the form of electromagnetic radiation. In other words, energy has become light, carried by photons, traveling outward towards the surface.

Though, not as dense as the core, the radiative zone remains extremely dense. In fact, core-generated light takes around 100,000 years to bounce through the radiative zone.

Convective Zone

Layers of the Sun Explained Convective Zone

Finally, light energy reaches the outer-most layer of the Sun’s interior, the convective zone. Now, density becomes low enough for light to convert into heat.

The newly-formed heat slowly cools as it rises toward the Sun’s surface. Eventually, as it cools enough, it falls back down toward the radiative zone, heating up once more. This rise-fall cycle, known as convection, continues repeatedly.

As energy rises, cools, falls and heats, it forms gigantic bubble patterns, known as convection cells. We see a similar process happening in a pot of boiling water. As the water boils, rolling bubbles of hot water form, like convection cells.

 

Layers of the Sun Explained – Exterior

Now, we can burst free and explore the Sun’s exterior. Three layers also comprise the Sun’s atmosphere: the photosphere, chromosphere and corona.

Photosphere

Layers of the Sun Explained Photosphere

Greek for “light sphere,” the photosphere is the layer of the Sun that we are most familiar with, usually through pictures.

Sun Sunspot

Visible light first appears in the photosphere. Though, unsafe to look at, the photosphere is where our human eyes see the Sun’s light, and brightness. Also, this layer is covered in the skin-like granules, caused by convection cells beneath. In fact, these granules last only around eight minutes, causing the constantly changing surface patterns on the Sun.

Temperatures in the lower photosphere are around 11,000º F, whereas temperatures near the top stay around 6,700º.

Also, sunspots occur within the Sun’s photosphere. Appearing as darker regions, sunspots last for several days, maintaining temperatures 3,600º lower than their surroundings. In fact, a sunspot’s center, is thousands of times stronger than the Earth’s magnetic field.

Chromosphere

Layers of the Sun Explained Chromosphere

Next, beyond the photosphere lies the chromosphere. This complex layer extends outward for over 3,000 miles.

Now, temperatures in the Sun’s chromosphere suddenly jump from 10,000º Fahrenheit to around 36,000º. At temperatures this high, hydrogen atoms radiate as rich red colors. Therefore, the red emissions give this layer its name, which is Greek for “color sphere.”

Sun's Chromosphere

Actual image captured of our Sun’s chromosphere.
Photo: JAXA/NASA

The chromosphere appears faint against the bright photosphere background. Typically, to visually see this layer and its activity, special equipment is required. Using solar telescopes and spectrographs, for instance, can reveal features such as dark filaments, magnetic field lines and more.

However, such advanced equipment can be both expensive and complicated to use. But, with simple and inexpensive eyeglasses, the chromosphere can be viewed by anybody during partial and total solar eclipses.

Corona

Layers of the Sun Explained Corona

Finally, we reach the Sun’s corona, Latin for “crown.” Similar to the chromosphere, the elusive corona is most often visible during an eclipse. This layer appears as a white crown around the Sun, which is actually hot plasma.

Solar Eclipse Corona

Strangely, temperatures in the corona swell to nearly 2 million degrees Fahrenheit! At these temperatures, elements like hydrogen and helium are stripped of their electrons, leaving a bare nucleus. Only much heavier elements, like iron, are capable of staying intact. Ultimately, the energy from the stripped electrons causes the staggering temperatures in the corona.

However, the corona provides several fascinating and interesting features. For instance, large spikes of plasma, called streamers, jut far out from the Sun. Plasma trapped by the Sun’s magnetic fields creates the spike shapes.

Perhaps most notable, the corona is ultimately responsible for our aurora borealis on Earth. As charged particles flow outward from the corona, they travel far into space. In fact, the winds carry far beyond Neptune, and even Pluto. And, as some of the powerful solar winds hit Earth’s atmosphere, they interact with gases and elements. These interactions are responsible for the ethereal and colorful auroras we enjoy here on Earth.