The Structure of the Sun

By Eman Abdallah Kamel

Eman is a writer and engineer. She is interested in searching for and writing about geography and astronomy. And many other topics.

In this article, you will learn about the composition of the sun, its elements, and the different layers of the sun, including the inner and outer layers.

The sun consists of layers composed almost entirely of hydrogen and helium. Image source: science.nasa.gov/gallery/

The Sun

The sun is a star. It is a huge, spherical body composed of hydrogen and helium. Its diameter reaches 1,400,000 kilometers. The sun is 109 times the diameter of the Earth. But it is four times less dense than Earth due to its structure.

A solar star is one of about 100 billion stars in our galaxy, the Milky Way.

The sun is not a solid mass. Unlike rocky planets like Earth, its borders are not easily identifiable.

The distance between Earth and the Sun is approximately 150 million kilometers (93 million miles). This distance is known as the astronomical unit (AU).

Our planet depends heavily on the sun. It regulates the seasons, climate, weather, and ocean currents. It also enables photosynthesis, which supports plant life. Without the sun’s heat and light, life on Earth would not exist.

God Almighty mentioned the sun thirty-five times in the Holy Qur’an. There is also a surah in the Quran called Ash-Shams, “The Sun.”

Let’s explore the composition of this interesting star, without which life on Earth would be impossible.

Composition of the Sun

The fact that the sun consists mostly of hydrogen and helium was first demonstrated in 1925.

Most elements in the sun are atoms, with a few molecules, all gases. The sun is so hot that no substance can remain liquid or solid. Due to the sun’s extreme heat, many atoms ionize and lose one or more electrons. It causes many free electrons and positively charged ions in the sun. Scientists call this state hot ionized gas plasma.

In the 19th century, scientists observed a 530.3-nanometer spectral line in the sun’s outer atmosphere, called the corona. It was not until 60 years later that astronomers discovered this emission was due to highly ionized iron (iron with 13 of its electrons stripped off).

Abundance of Elements in the Sun

Element	Percentage By Mass
Hydrogen	73.4
Helium	25.0
Carbon	0.20
Nitrogen	0.09
Oxygen	0.80
Neon	0.16
Magnesium	0.06
Silicon	0.09
Sulfur	0.05
Iron	0.14

The sun and its atmosphere consist of many layers. Image source: nasa.gov

The Different Layers of the Sun

The sun consists of:

1. The Inner Layers are

The Core
Radiative Zone
Convection Zone

2. The Outer Layers are

The Photosphere
The Chromosphere
The Transition Region
The Corona

1. The Inner Layers

The Core:

All of the energy in the sun comes from its core. The material that makes up the core is very dense because of the extremely high pressure and temperature (the core has temperatures higher than 15.7 million Kelvin, equivalent to 28 million degrees Fahrenheit or 15.7 million degrees Celsius). It is the combination of these two properties that creates an environment where nuclear reactions can take place. These reactions always produce heavier elements on the periodic table.

Did You Know?

The core is the central zone where nuclear reactions consume hydrogen to form helium. These reactions liberate the energy that eventually leaves the surface as visible light.

The Radiative Zone:

It extends outward from the core’s outer edge to the convection region’s base. Through this region, in the form of radiation, energy is transmitted through its interaction with molecules in the surroundings.

Some atoms can remain intact in the radiation zone because the temperature is slightly lower than in the core. These particles can absorb energy, store it briefly, and release it as new radiation.

There is a tachocline area between the radiative and convective zones. This region is the result of the sun’s differential rotation.

The Convection Zone:

The outer layer of the solar interior extends from a depth of about 200 thousand kilometers to the visible surface, where its movement appears in the form of grains and supergrains.

In this region, the sun’s temperature is not hot enough to transfer energy by thermal radiation (2 million degrees Kelvin). At this temperature, atoms will absorb energy more readily, but because their surroundings are dense and cold, they will not release it as readily. Therefore, the transfer of energy by radiation slows down considerably. Instead, it transfers heat by convection through thermal columns.

The Solar Dynamics Observatory (SDO) observed three X-class flares on the Sun between February 21 and 22, 2024.

2. Outer Layers

The Photosphere:

We can directly observe the photosphere, the lowest layer of the Sun. It extends roughly 250 miles (400 km) above the solar disk’s center, where it meets the visible surface. The photosphere has a temperature range of 6,500 K at the bottom and 4,000 K at the top.

Despite being the product of processes and disturbances in other solar layers, sunspots, solar flares, and solar prominences form in the photosphere.

Did You Know?

Sunspots are dark, cool areas on the Sun’s surface that can move, change, and disappear over time, but solar flares are explosions in the Sun’s atmosphere that release charged particles and a wave of energy into the solar system. Solar prominences are huge explosions of cold gases from the surface of the Sun in the form of a giant ring.

To learn more about sunspots and solar Flares, visit spaceplace.nasa.gov

The Chromosphere:

It is an irregularly shaped layer above the photosphere, where the temperature rises from 6000 degrees Celsius to about 20 thousand degrees Celsius.

The chromosphere releases jets of burning gases called spicules. These fiery wisps of gas extend from the atmosphere like long, flaming fingers. They are usually about 500 kilometers (310 mi) in diameter. The spicules last only 15 minutes but can reach thousands of kilometers in height before they collapse and melt.

Did You Know?

The chromosphere is thicker than the photosphere and has a very low density; it’s impossible to observe it without narrowband filters or during a total solar eclipse due to the brightness of the photosphere behind it.

Transition Region:

The transition zone is a very narrow layer (60 miles/100 km) between the chromosphere and the corona, where the temperature rises suddenly from about 8,000 to about 500,000 K.

The Corona:

It is the sun’s outer atmosphere. It is the largest and least dense structure of the Sun. The corona is composed of plasma escaping from the sun, whose intensity reaches 1,000,000 Kelvin. Only during a total solar eclipse can one see the corona.

The solar wind is the outflow of coronal gas that lies beyond the corona. The sun’s magnetic fields rise through the convection zone and erupt through the photosphere into the chromosphere and corona. The explosions give rise to solar activity, such as sunspots, flares, protrusions, and coronal mass ejections.

What is the meaning of a coronal mass ejection?

Coronal mass ejections (CMEs) are large ejections of plasma and magnetic fields from the sun’s corona. CMEs from the sun travel outward at speeds ranging from as slow as 250 kilometers per second (km/s) to nearly 3,000 km/s.

The fastest coronal ejection reaches Earth in less than fifteen to eighteen hours. Slower CMEs can take many days to arrive. They expand as they spread away from the sun, and larger coronal ejections can reach a size that encompasses nearly a quarter of the area between the Earth and the sun by the time they reach Earth.

Sources

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