The journey of energy out of the Sun

This section goes into more detail on some of the main zones (differentiated by the main form of energy transfer taking place), between the core and the Sun's outer surface; describing the main reactions, occurring as energy slowly travels outwards, before finally being released into outer-space.

The Radiation Zone

Within the Radiation Zone, the Positrons quickly encounter high attraction collisions with the many free electrons (it’s antiparticle with a negative charge), annihilating both, and giving off two or more Gamma Ray Photons in the process. Unlike the Positrons, however, all the expelled Gamma Photons are not destroyed, instead their energy is radiated (transferred) through the absorptionemission and scattering of photons in the Radiation Zone Plasma.

Magnetic Dynamo

The Radiative Zone together with the Core rotates faster than the surrounding Zones (this is possible as the Sun is made up of plasma & gas, and is not a solid). Scientists believe this speed differential creates a very large shear, at the area of contact between these two layers, generating a huge Magnetic Dynamo – the dipolar magnetic field for the Sun (which flips its' North and South on a 11 year cycle). This area of immense shear is known as the Tachocline.

Convection Zone

After the Tachocline transition zone is the Convective Zone. Here, the visible light Photons' energy is sufficiently low, so that they can be absorbed by the solar plasma in the subsequent Convective Zone. They are not directly released, which makes the solar plasma atoms and ions (known as Granules) extremely hot. This heat makes the Granules rise to the surface – to the Photosphere – where they release their excess energy (again as Photons) creating a bubbling visible effect on the surface of the Photosphere, known as Granulation. As the energy is released, the Granules cool and then subsequently sink back down to the base of the Convection Zone, to repeat the process again. This process has been compared to a giant lava lamp.


As described below, the Sun has other layers above the Photosphere, however, it can be classed as the outer shell, as it is the first (lowest/deepest) surface of the Sun that is perceived to emit light. Below this layer, the plasma is opaque.

Atmosphere: Chromosphere, Transition Region, Corona, and Heliosphere

The atmosphere is composed of four distinct parts. The first, the Chromosphere, which is the 'coloured flash' that is visible at the start and end of a total solar eclipse. It is usually only visible during an eclipse, as it is not very dense, and is out-shone by the photosphere below. Many complex and dynamic phenomena, such as coronal mass ejections and coronal loops, discussed below, can be observed in the Chromosphere.

The second part of the Sun's Atmosphere, is the Solar Transition Zone. It is visible with ultraviolet sensitive telescopes, and marks the differences between the Chromosphere below and the Corona above such as: most of helium is not fully ionised below, but is above; and gas pressure and fluid dynamics seem to dominate below, however magnetic forces seem to dominate above.

The Corona is the next part of the Sun's Atmosphere. Unlike all the other layers of the Sun that get cooler the further they are from the core, the Corona actually gets much, much hotter than the visible surface of the Sun, although it is still not clear why. During quiet periods, the Corona is mainly gathered around the Sun's equator, however, during active periods, it spreads across different parts of the Sun's surface (particularly near sunspots).

And it is here that Solar Winds are formed, as superheated protons and electrons (‘smashed’ atom plasma) collect and leak out of the corona, at a rate of 7 billion tonnes per/hour, travelling at supersonic speeds.

Finally, the Heliosphere, is the outermost atmosphere of the Sun, which includes the solar wind plasma. It is described as an immense magnetic bubble-like region, which extends beyond Pluto, with its outer boundary, roughly defining the edge of the heliosphere and the interstellar gas outside the solar system.

Solar Activity: Coronal Mass Ejections, Coronal Loops, and Prominences

As well as a differing rotation speed between the Radiative Zone and the Convection Zone, the Sun also rotates at a different speed at the Equator than at the two Poles (due to it plasma like properties). This helps maintain the Magnetic Dynamo, and is also believed to twist the magnetic fields together, which over time, eventually erupt from within the Tachocline and through the Photosphere. These escaping magnetic fields form loops filled with plasma, known as Coronal Loops, and are thought to generate the Sun's intense Sunspots and Prominences.

The Sunspots appear dark on the Sun’s surface, as they are cooler than the surrounding plasma within the Photosphere (the high magnetic energy of the Coronal Loop inhibits convection), and also due to their large size (as large as 80,000km) they are visible from Earth. Prominences project out cool plasma into the Sun’s very hot exterior atmosphere – the Corona. Here they can break up and eject Gamma Rays, X-rays and Ultraviolet Rays out into space.

The Coronal Loops can also become twisted and finally break (known as Solar Flares) as they spontaneously reconfigure themselves into simpler forms, giving off energy that can also eject Gamma, X, and UV Rays into space. Of those very hot photons that were projected towards Earth, when they arrive, they can cause severe disruptions of the Earth’s upper atmosphere, creating such things as the Aurora Borealis (Northern Lights) and Geomagnetic Storms.

Coronal Mass Ejections (CME's) often follow from Solar Flares, and are usually large releases of plasma and magnetic fields from the Corona.Whilst Solar Flares are very fast, CME's are relatively slow - but have powerful effects on Earth's magnetosphere.


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