Sun is Life giving star of our solar system. Born nearly 4 - 5 billion years ago, situated at 26,000 light years away from the centre of the galaxy (galactic core) Sun is an average star of our galaxy Milky-Way. There are 200-400 billion suns in Milky-Way. About size of Sun, it has 110 times the diameter of Earth (~1.4million Km) and about 1 million spherical Earths could fit in the Sun. It has 8 planets millions of asteroids and other objects known as Small Solar System Bodies.
About its origin, it is believed that Sun is Population I type star because it has elements heavier than helium. Scientists believe Sun and whole solar system was formed by a giant rotating cloud of gas. It was collapsed due to its gravity and created all the planets & the Sun.Like Earth rotate around the Sun, Sun itself (hence the whole solar system) rotate around the centre of Milky-Way Galaxy at 220kms and it takes 250 million years to complete one orbit.
Chemistry of Sun is consist of mainly Hydrogen and Helium around 74% Hydrogen & 25 Helium and less than 1% other heavy elements. Sun has 6 layers, starting from inside these are- The Core, Radiative zone, Convection zone (these are not visible), the visible part of surface known as Photosphere, Chromosphere and finally outermost region Corona. First four layers are collectively form our Sun and last two are the outer region above the Sun’s surface. Core is most dense region of the Sun, it holds nearly half of the total mass of the Sun. Light photons are created at the centre of the Sun by nuclear reactions under intense pressure and temperature conditions (more than 10million C). Photon releases by these reactions than start their journey towards Sun’s surface and then towards us and endless universe. These photon takes 10,000 to 1, 70,000 years (because density is very high at core & Radiative zone) to travel distance from Sun’s core to its surface and then 8 minutes and 20 seconds from surface to us.
Back to Sun layers, radiative zone extends from core to the Sun’s surface and complete 70% of the Sun. It holds nearly 48% of the total mass. The convection zone reaches up to the sun's surface holds only 2% of total mass. Photosphere is visible surface of the Sun. It is the point where light photon end their journey inside the Sun and start their outer or free journey into space. Sun has two layers which are well above its surface Chromosphere and Corona. Light emitted by these layers are not visible because it is too hard to be seen against the brighter photosphere. It can be seen during total solar eclipse when photosphere is covered by the Moon. Photosphere temperature increases as altitude increases and can go as high as 2million degrees C, this is really amazing and mysterious and astronomers are still searching for correct explanation.
Temperature at the surface is not equal, it varies, some part are has lower temperature as compare to neighbouring area hence they look some darker and known as Sunspots. These areas have strong magnetic fields. These Sunspots are part of 11year magnetic activity cycle. They can have temperature up to 3000 – 4000 degree C. Physicists are still seeking more information to know reasons behind Sunspots generation and their movements etc.
So you see Sun still have many mysteries inside it, full understanding and knowledge of these will help us to learn more about other stars.