# Our Sun

The sun is a star. It is kind of a strange statement to say but since it is glowing so close to us we sometime forget that is just same kind of object like others. The Sun is very close to us and other stars are very far away so they are fainter. Sun is a yellow star with good size as the majority of stars in the universe are dim red dwarfs far smaller than the sun. It should be noted that by size and number, Sun ranks in top 10% of stars in the galaxy. In solar system, it is the most dominating and influencing factor.

Our sun is big hot ball of hydrogen gas which is 1.4 million km across and is 100 time the diameter of Earth and so big that over a million Earths can fit inside it. Its mass is 300,000 times more than that of the Earth. The core of the Sun is pretty unimaginable. The pressure there is 260billion times the earth’s atmospheric pressure and temperature reached to 15 million degrees Celsius. In this extreme condition, hydrogen is in ionized state and electron floats separately from the protons. So, the core of the sun is a hot soup of subatomic particles.

In these extreme condition, the protons fuse together to form Helium along with the release of energy stored in the atom. The amount of energy release is given by Einstein’s famous equation $E=mc^2$. In this reaction mass is converted into energy. It is estimated that the Sun converts 700 million tons of hydrogen into 695 million tons of helium every day. This missing 5 million tons are converted into energy. To compare, this energy produced is equivalent to detonating 400 billion one megaton nuclear bombs every second.

It should be noted that nuclear fusion happens in the core of the Sun as the gas above the core is not quite hot enough to fuse hydrogen into helium. More we move from the core, less dense the gas becomes. The heated gas in the core moves upward and hence transfers the heat by the process of convection. This is an efficient process to bring the Sun’s internal heat to the surface. There is a layer called the photosphere above the convecting layer. At this point the density of material inside the sun becomes small enough to become transparent. Since sun is a gas, no solid surface is marked but we can take photosphere as sun’s surface. There is another layer above photosphere called corona which is less than 1% as dense as photosphere but is much hotter and temperature can reach up to million degrees. It’s very faint to observe from earth but it can be seen during a total eclipse or through some special telescope. Corona extends for millions of kilometers.

Solar wind is another interesting phenomena which is made up off subatomic particles moving away from the Sun. It blows in all direction and its speed reaches about a million kilometers per hour. The light produces in the core is immediately absorbed by subatomic particles and this increase the velocity of the particle with re-emission of slightly less energetic light. The light travels this way out of the Sun losing energy every time. This process is called random walk of photons. A more careful calculation has shown that the light produced in the core takes close to 200,000 years to come to the surface.

Another exciting phenomena happening in the Sun is its magnetism. The plasma state of matter in the Sun is responsible for magnetic field as in this state, electrons and protons are separated and are moving at high speed. Sunspot are a result of plasma and magnetic field interaction and these spots can be very huge and easily dwarfs earth in size. There are huge magnetic field loop created on the surface of the sun and this loops can snap and explode resulting in what we called solar flare. Solar flare can be extremely powerful and can release huge amount of energy along with launching material off the surface of the Sun at high speed. CME or coronal mass ejection is another localized event and occurs higher off the Sun’s surface. It also ejects materials into space. There ejected material can reach Earth and has some profound effects. Earth’s atmosphere absorbs high energy light and deflects subatomic particles via its magnetic field.

Poles of the earth is highly effected by this phenomena and causes the air to glow. This light is called northern or southern light. This spectacular show of light is amazing. It should be noted that even though earth can prevent small surge of the flare massive surge can create some problem like overload power grid, satellite circuit damage etc.