Sun – Internal Structure and Atmosphere

In the previous articles, we got to know about the formation of the Sun and the Solar System. We know that our Solar System consists of the Sun, eight major planets, some dwarf planets (like Pluto, Ceres, etc.), many satellites, countless minor planets, asteroids, and debris.

And the Sun is the gravitational center of our Solar System. Carrying on the same sequence, today we will extensively focus on the Sun. We will learn about the internal structure and the atmosphere of the Sun.

 

Firstly, Let’s talk about the significance of the Sun

If we talk about the universe, the Sun is just an ordinary star. There are far bigger and brighter stars in the universe.

But at our level, the Sun is certainly the most important star in the whole universe not only because it is the reason for our existence but also because it is the reason for our survival. The Sun satiates almost all of our energy requirements.

Some facts about the Sun

• The Sun is 4.6 billion years old and has a diameter of 1.39 million kilometers. It is the largest object in the solar system.
• The temperature of the core of the Sun is estimated to be more than 15 million K due to continuous thermal nuclear reactions while the surface temperature being 6000 K.
• The Sun accounts for about 99.8% of the total mass of our Solar System.
• A huge ball of burning gases, and made up of nearly 73.4% Hydrogen and 25% Helium.The Sun rotates in the counterclockwise direction (considering the view from a long way above of the North Pole of the Earth) and has a rotation period of 25 days and 9 hours.
• The Sun finds its personification in many mythologies with different words. In Indian mythology, it finds its name as Surya, in Greek as Helios, in Romans as Sol, etc.
• The Sun shows the phenomenon of differential rotation. At the equator, the surface rotates in 25.4 days and near the poles, it rotates in 36 days. This strange phenomenon occurs because the outer surface is not solid, and the core is solid. Same phenomenon occurs in the outer gaseous planets.
• The magnetic field of the Sun is very strong and encircles the whole Solar System.
• The heat output of the Sun is variable. As a comparison, now the heat output is 40% more than the heat output during the birth of the Solar System.
• The Sun is nearly at its midlife. Its Hydrogen fuel can sustain for more than 5 billion years. After that, it will undergo extreme changes and the Earth will vanish.

Internal Structure and Atmosphere of the Sun

The outer layers of the Sun form its atmosphere. There are mainly three layers that make up the atmosphere namely the photosphere, the chromosphere, and the corona.

The internal part of the Sun consists of the core, radiative zone, and the convective zone. In the outer layers, the energy produced in inner layers is detected as sunlight.

Atmosphere of the Sun

As mentioned above, the atmosphere is made up of layers such as the photosphere, the chromosphere, and the corona. Let us discuss them, one by one-

Photosphere

• All the visible light from the Sun comes from the Photosphere.
• It has a thickness of about 500 KM.
• It is the coolest part of the sun with temperature coming down to 5500 0C.
• The temperature drops with an increase in height.
• Phenomenon such as Sunspots occurs in the photosphere.

Sunspots

• Sunspots are the dark spots on the Sun’s surface.
• They are formed due to magnetic fields and the region becomes cooler (about 500 – 1500 0C) and darker than the surrounding.
• Lifetime of sunspots varies from a few days to a few months.
• The center of sunspot is known as Umbra. The lighter region of surrounding is known as Penumbra.
• It believes that the Sun is 1% cooler in the absence of Sunspots. The absence of Sunspots might affect the Earth’s climate.
• The number of Sunspots changes every 11-year due to the Sun’s magnetic activity cycle.

Chromosphere

• The Chromosphere lies just above the Photosphere.
• The visible light from the chromosphere seen only during Solar Eclipses when the Photosphere is hidden.
• It is visible as a red dim ring.
• The temperature increases with the increase in height.

Corona

• The Corona layer lies above the Chromosphere. It is the outermost layer of the Sun’s atmosphere.
• It is visible during a total Solar Eclipse as a glowing white corona.
• The temperature on the Corona reaches up to 2-million-degree Celsius, the reason of which is still unknown.
• The phenomena associated with Corona are Coronal Mass Ejection, Solar Flares, and Solar Winds.

1. Coronal Mass Ejection (CME) is the release of plasma and magnetic field in a large amount.
2. Solar Flares are the instantaneous flash of increased brightness which occurs when magnetic energy is suddenly released
3. Solar Wind is the flow of energized, charged particles at a very high speed. It is made up of plasma and mostly contains electrons, protons, and alpha particles.

• Coronal Mass Ejection (CME) is the release of plasma and magnetic field in a large amount.

Solar Flares

• Solar Flares are the instantaneous flash of increased brightness which occurs when magnetic energy is suddenly released.
• They occur due to magnetic anomalies.
• These are magnetic storms and heats anywhere between 10 to 20 million 0C.

Solar Winds

• Solar Wind is the flow of energized, charged particles at a very high speed.
• The speed is as high as 900km/s at a temperature equal to 1 million 0C.
• It is made up of plasma and mostly contains electrons, protons, and alpha particles.

Effects of solar winds:

• On Earth, the phenomenon of Aurora happens due to the magnetic field lines of the Earth and solar winds.
• The charge carrying particles enter the atmosphere which cause the ionization and excitation of atmospheric constituents and consequently optical emissions.
• When the solar winds approach a planet with a proper magnetic field, the field deflects the particles of solar winds.
• This extent of the spread of the magnetic field called the magnetosphere. Its boundary is magnetopause.
• The solar winds are primarily responsible for the shape of the Earth’s magnetosphere.
• When the magnetosphere is weak enough then the solar winds strip off the atmosphere of that planet.
• The atmosphere of Venus is 100 times denser than the Earth’s atmosphere, with little geomagnetic field. This is somewhat unusual.

Solar Prominence

• A solar prominence is a huge arc that hangs to the surface of the Sun.
• It anchors from the photosphere to Corona. Plasma makes up the Solar Prominence.
• A prominence holds up its position by strong magnetic field lines.
• An unstable prominence may last for a day, but the stable ones last for months.
• It holds up hundreds of thousands of miles in the Solar System.
• When an unstable prominence erupts, it releases a lot of solar material, primarily plasma.
• The reason for the origin and existence of solar prominence is still unknown.

Plasma

• Plasma is one of the natural states of matter along with solid, liquid, and gas.
• It contains ionized gases.
• It is normally observable in lightning and electric sparking.
• Plasma lamps are the application of Plasma. In these lamps, the production of light happens due to the excitation of plasma. Generally, these lamps use a noble gas or mixture of noble gases.

Composition of Sun’s Atmosphere

All the stars have a similar composition in the terms of elements present. A star’s absorption line spectrum helps us to determine its composition.

Hydrogen and Helium are the most abundant elements in the Sun. Both of them combined account for more than 98%. But a lot of other elements are present in the Sun’s atmosphere.

The table below provides the information about the top 10 elements present in the Sun:

Element	Percentage by mass
1. Hydrogen 2. Helium 3. Carbon 4. Nitrogen 5. Oxygen 6. Neon 7. Magnesium 8. Silicon 9. Sulfur 10.  Iron	73.4 25.0 0.2 0.09 0.8 0.16 0.06 0.09 0.05 0.14

Internal Structure of the Sun

As stated earlier, the interior of the sun consists of the core, radiative zone, and convective zone. It is the part where energy generation occurs. Let us look at the layers of the interior of the Sun.

Core

• The core is the centermost region of the sun.
• It is the region where the nuclear reactions occur, and the Hydrogen turns into Helium by nuclear fusion.
• It is the hottest region of the Sun with temperatures believed to be reaching more than 15 million degrees Celsius.
• The density at the center of the core is about 150 g/cm3 and 20g/cm3, near the radiative zone. The density and temperature decrease when we move towards the outward layers.

Radiative Zone

• The Radiative zone lies between the core and the convection zone.
• In this layer, the energy transports toward outside by the means of radiative diffusion and thermal conduction, rather than convection.
• Energy travels in the form of electromagnetic radiation by photons.
• Photons bounce from particle to particle and transfer energy.
• The density decreased from 20 g/cm3 to 0.2 g/cm3 at the edge of the radiative zone.

Convection Zone

• It is the outermost layer of the Sun’s interior.
• It gets its name from the mode by which energy transfer takes place in this region, i.e., Convection.
• At its base, the temperature is about 2 million degrees Celsius.
• The temperature is low enough or the region is cool enough for the heavier ions (like carbon, oxygen, nitrogen, iron, and calcium) to hold on some of their electrons.
• This hold up makes the layer opaque and makes it harder for the radiations to get through which traps the heat and makes the fluid unstable resulting in boiling and convection.

Conclusion

In this article, finally we tried to achieve a good understanding of the star of our own Solar System, the Sun. We learned about the significance of the Sun. After that, we talked extensively about the layers of the atmosphere of the Sun and also the layers of its internal structure.