The sun is a huge 5 billion-year-old ball of gas and Plasma. The sun is located at almost the centre of the solar system and it is a host star to the Earth. It has a radius of around 700,000 km (434000 miles) or a diameter of 1.4 million kilometers (868000 miles).
Birth and Nuclear Fusion:
How does the Sun shine? firstly, the sun is not set on fire. Like all stars, it shines bright and produces heat through a process called nuclear fusion. This process goes on in the heart (the core) of the sun. This process of nuclear fusion that gave birth to the Sun is estimated to have started 5 billion years ago. But, how does the process start?
All stars including the Sun formed when huge clouds of hydrogen gas collapsed under the influence of gravity. The sudden collapse gas caused them to heat up. This heat and pressure forced hydrogen atoms to start fusing into helium and oppose the collapsing gas. The outward force of nuclear fusion and inward force of gravity equal out at a point and a stable star is formed.
The nuclear fusion process emits photons of light that escapes the core of the sun and reaches us, here on Earth.
Main Sequence/present phase:
The sun is in its Main sequence phase. Main sequence stars are those stars that undergo hydrogen fusion to form helium in their core. The sun will remain in this phase for the next few billion years.
Red giant Stage:
5 billion years from now, the Sun is expected to exhaust its nuclear fuel- hydrogen. All of it will be converted to helium. When this happens, gravity starts to take over and the outer layers of the star crush the core. The pressure from the outer layers forces the helium to start fusing as well. An excess of nuclear energy is released and the outer layers start to expand exponentially. The Sun will engulf the planets mercury, Venus, and maybe Earth as well.
White dwarf Phase:
In about 10 billion years, the Sun will “shed” its outer layers forming a beautiful Planetary Nebula. Only the core will be left behind. This core is called a White Dwarf Star. In a few hundred billion years, this white dwarf star will lose its heat and light and will turn into a black dwarf star. This Black Dwarf will float in space until the death of the universe.