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Discover the layers of the sun, including the core, radiative zone, convective zone, photosphere, chromosphere, and corona.

Find out which layers you can see from Earth. Investigate what sunspots and solar flares are.

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Anatomy of the Sun

The inner layers of the sun
Sun Inner Layers

Our sun is the closest star to Earth and the source of energy for all life here. The sun has been so important to humans that it has been celebrated and worshiped since ancient times.

Ancient cultures built monuments to the sun, set up the calendar based on it, and took note of lunar and solar eclipses. The sun gets its name from the Romans, who called it Sol; this was translated into sun in modern English.The sun is essentially a huge burning ball of gas in the sky only 100 million or so miles from Earth. The majority of gas in the sun is hydrogen and helium, and it is so hot that all of these elements exist in the gaseous state. The gas is held together by gravity, which creates intense heat and pressure in the core. The sun has an interior consisting of the core, radiative zone, and convective zone.

It has a visible surface called the photosphere, then the chromosphere, which usually isn’t visible, and the very outer layer called the corona.

Inner Layers

Let’s start at the core of the sun and work our way outward. Like any hot ball of fire in the sky, the sun has an inner core.

This is where fusion occurs. The core is the very center of the sun where fusion occurs. The core has extremely high temperature and pressure. It is so hot here – 15 million degree Celsius – that nuclear fusion occurs. In the case of our sun, four hydrogen nuclei are fused into one helium nuclei while releasing a bunch of energy as photons. The sun produces so much energy that according to NASA, it can melt a block of ice one mile wide by two miles long in just one second. The core is the hottest part of the sun and the only part of the sun that produces much energy.

The sun cools off as you travel from the core to the outside, with the exception of the chromosphere.The next layer of the sun is the radiative zone, the layer of the sun directly above the core. This zone, as you can probably guess, emits radiation, and the radiation from the core diffuses out from here. It may take photons millions of years to get out.

The next layer as we work our way outward is the convective zone. In this layer, photons produced by fusion in the core make their way to the surface of the sun through convection.This zone is dominated by convection currents that carry the energy produced through fusion in the sun’s core outward to the surface. A convection current is when hot gas rises next to hot gas falling, which causes movement or currents. This energy is carried by photons which can take 200,000 years to move from the core to the sun’s surface. It then takes eight minutes for those photons to travel to Earth and provide us with energy.

Outer Layers

The first of the outer layers of the sun is the photosphere. This is the part of the sun that we see because it emits light in our visible wavelengths. This layer is about 300 miles thick, and the temperature has cooled to 5,500 degrees Celsius.

There is not really a ‘surface’ to the Sun, but this is the layer that we see that looks like it is the surface.

These three layers comprise the atmosphere of the sun.
Sun Outer Layer

The fifth layer of the sun traveling outward from the core is the chromosphere, a red layer of the sun that is 1,000 miles thick. This thicker layer of the sun emits light in the red part of the visible spectrum. The temperature rises greatly here, which is unique.

Everywhere else on the sun, temperature decreases as you move further away from the core, but in this layer the temperature increases. This layer is only visible during solar eclipses.The outermost layer or atmosphere of the sun is the corona.

This is the sun’s atmosphere, and it has temperatures near one million degrees Celsius. The corona is millions of miles thick above the photosphere, and most of the time we can’t see the corona because the photosphere is too bright. It can only be seen during a solar eclipse, when it looks like a spiky white ring. This is similar to Earth’s atmosphere, which we can’t see, but we know it is there.

Sunspots and Solar Flares

Solar flares erupt in the chromosphere.
Solar Flares

The other two terms you may have heard of with regards to the sun are sunspots and solar flares.

A sunspot is a temporary dark spot on the photosphere layer of the sun that is caused by magnetic activity. The spots appear dark because that area is cooler than the surrounding photosphere. A solar flare is a sudden and tremendous eruption in the solar chromosphere.

Solar flares release tremendous amounts of energy. These flares can disrupt long-distance radio communications on Earth.

Lesson Summary

The sun has six layers. Three layers, the corona, chromosphere, and photosphere, comprise the sun’s atmosphere or outer layer. The other three layers, convective zone, radiative zone, and core, comprise the inner layers, or the parts of the sun that are not seen.

The sun has ‘blemishes’ on its surface, known as sunspots, which are temporarily cooler spots on the surface of the sun, and solar flares, which are enormous explosions on the surface of the sun.

Learning Outcomes

  • Identify and describe the three inner layers and three outer layers of the sun
  • Define sunspot and solar flare

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