The Sun

Humans have always been curious about the Sun. Though people lived with myths for a long time, it's been twenty-five hundred years since the first time the philosophers from Greece conjectured that Sun is a star. Mankind took millenia to confirm that. Roughly five nhundred years ago, the historical trio of Copernicus, Galileo and Kepler broke the geocentric model. Since then, there has been huge leaps in technology and the understanding of the Cosmos. Hans Bethe, for instance, had drawn the cycle of fusion processes that happen in stars by 1940. With the help of numerous such contributions, eighty years later, in the present, we have the most sophisticated model of the Sun that has ever been created. Some intriguing questions for us are - How do we study the Sun? How does Sun look like under the surface? While this article is focused on the second question, specifically the inner regions of the Sun, some references for first question are given as well. The present day Solar model divides the Sun into an interior and an atmosphere. The interior is further divided into a core, a radiative zone and a convective zone. The core however is the main powerhouse of Sun with the most density.The hydrogen fusion that fuels the star essentially happens in the core. With a whopping 15 million K of temperature, the matter existing there stays in plasma state. The core is composed of 33% hydrogen, 65% of helium and 2% of other elements. The amount of hydrogen in core eternally reduces by fusion until the Sun reaches a transition stage in its lifecycle. Roughly 600 million tonnes of hydrogen atoms are converted into helium every second and the mechanism behind it is mind bogglingly complex. The solar core engages in the p-p chain reaction for fueling the Sun. In this process 4 Hydrogen atoms fuse into single helium nucleus.

Where the first reaction takes a billion years due to the involvement of weak force. The next two reactions by contrast just take 4 seconds and 400 years on average,respectively. This is due to the strong force interactions. As a result 3.86 x 10^26 J of energy is released per second from the core. The radiative and convective zones merely transfer the energy released from the core. The energy released in the form of neutrinos pierce through any matter and escape the Sun easily. EM waves transfer through Radiative diffusion and thermal conduction. The EM waves(energy) from core reach the dense radiative zone and get scattered and absorbed continuously by the particles before travelling a short distance. As a result it takes approx.171000 years for gamma rays to escape this zone. The temperature reduces from 15 million K to 1.5 million K at the base of convection zone. In the convection zone, as the name suggests, the energy from the EM waves escaping the radiative zone are transferred to the Solar atmosphere through convection. This convection consists of mass movement of plasma forming a circular convection current with the heated plasma ascending and the cooled plasma descending. The transition region between the radiative and the convective zone is called tachocline from where the magnetic field of the Sun is thought to be originating.Basically all the sunlight that we get from the Sun undergo all this process before reaching us.

And that concludes a brief description of Solar interior. Thanks to the staggering amount of information collected about Sun by the mankind, the Depiction of Sun by a Model is possible and hopefully the exploration is never going to be bounded.