Sol – Our Sun

The Sun has very distinctive chemical features. The Chemical composition of Sun at the time of formation was about 99.9% hydrogen. With nuclear fusion process for billions of years, the hydrogen got fused together to form helium. Helium is heavier gas and hence settles towards the centre region of the Sun known as core. The Sun contains about 90% Hydrogen and 10% helium by count whereas 75% hydrogen and 25% helium by mass.

Sun has 6 distinctive zones:

⬥ Core

The core is the innermost layer of the sun and it is a source for all the Sun’s energy. The material in the core is firmly attached and has very high temperature, which is about 15 million degrees Kelvin. In the core the intense heat destroys the internal structure of an atom and therefore all atoms are broken down into their constituent parts. An atom is composed of protons, electrons and neutrons. Neutrons have no electric charge and so they do not interact a lot with the surrounding medium. Thus neutrons go away the core fairly and quickly. The protons, which have positive electric charge, and the electrons, which have negative electric charge, remain in the core and force the reactions which fuel the Sun. The charge neutral material of protons and electrons that makes up the core is called plasma. The high temperature provides the protons and electrons with a great amount of thermal energy and therefore they moved pretty quickly and they combine with the high density of the plasma, causes the particles to continuously slam into one another creating nuclear reactions. It is the fusion, or slamming together, of particular combinations of particles that provides the energy source of the Sun.

Thermonuclear reactions takes place inside the core ,thus hydrogen atoms are comnbined with each other to make helium atoms and produces energy which keeps the Sun in a state of equilibrium.Thus this thermonuclear reaction is called nuclear fusion.

⬥ Radiation Zone

Once the energy is produced in the core of the sun, it has to travel from the solar center to the outer regions. Hence the radiation zone provides an efficient means of transferring energy near the core. The temperature in the radiation zone of the sun is cooler than the core. The material 0.2 to about 0.7 solar radii is hot and dense enough that thermal radiation is sufficient to transfer the intense heat of the core outward. Heat is transferred by ions of hydrogen and helium emitting photons, which travel a brief distance before being re-absorbed by other ions.

⬥ Convection Zone

Ranging from 0.7 solar radii to 1.0 solar radii, the material in the Sun is not that much dense or hot to transfer the heat energy from interior to outward. Hence, thermal convection occurs as thermal columns carry hot material to the surface (photosphere) of the Sun. As soon as the material cools off at the surface, it plunges backside downward to the base of the convection zone, to obtain more heat from the top of the radiative zone. Convective exceed is thought to occur at the base of the convection zone, moving turbulent down flows into the outer layers of the radiative zone.

The thermal columns in the convection zone shape mark on the surface of the Sun, in the form of the solar granulation and supergranulation. The turbulent convection of this outer part of the solar interior gives rise to a ‘small-scale’ dynamo that produces magnetic north and south poles all over the surface of the Sun.

⬥ Photosphere

Photosphere is the visible surface of the Sun. Above the photosphere, sunlight is free to disseminate into space and its energy escapes the Sun completely. Sunlight has approximately a black-body spectrum that indicates its temperature is about 6,000 K, interspersed with atomic absorption lines from the tenuous layers above the photosphere. The photosphere has a element density of about 1023/m3 (this is about 1% of the particle density of Earth’s atmosphere at sea level). The parts of the Sun above the photosphere are referred to collectively as the solar atmosphere. They can be seen with telescopes across the electromagnetic spectrum, from the visible light to gamma rays.

⬥ Chromosphere

This a thin layer present above the visible surface, which is about 2,000 km thick, specifically dominated by a spectrum of emission and absorption lines. It is called the chromosphere from the Greek root chromos, meaning color, for the reason that the chromosphere is visible as a colored flash at the beginning and end of total eclipses of the Sun.

⬥ Corona

The corona is the outer atmosphere of the Sun, which is much larger in volume than the Sun itself. The corona merges slickly with the solar wind so as to fill the solar system and heliosphere. The low corona, which is very close to the surface of the Sun, has a particle density of 1011/m3 (Earth’s atmosphere near sea level has a particle density of about 2×1025/m3). The temperature of the corona is several million degrees K.