The Sun is also a star which is very near to us, that is why it looks bigger than other stars.
The nearest stars after Sun are part of a star system more commonly known as the Alpha Centauri star system. It consists of three stars, one red dwarf and two stars similar to our own star, the Sun. The red dwarf is Proxima Centauri (4.23 Ly) and is the second closest star to Earth (or closest when you exclude the Sun). Proxima, its name means Proximate and cannot be been seen without a telescope or a pair of binoculars. Alpha Centauri A (4.32 Ly) and B (4.37 Ly) are the next closest at positions three and four in the list. They are located in the southern constellation of Centaurus. (Ly stands for light year.)
The Sun is a nearly perfect sphere of hot plasma held together because of its gravity and mass. It’s incandescence is because of the nuclear fusion reaction radiating the energy mainly as visible light, ultraviolet light, and infrared radiation. It is the most important source of energy for life on earth. Its diameter is about 1.39 million kilometres or 109 times that of earth (12,756 kilometres). Its mas is about 330,000 times that of earth. Three quarters of the Sun’s mass is that of hydrogen (73 %), the rest is mostly helium (25%), with much smaller quantities of heavier elements including oxygen, carbon, neon and iron.
The Sun is a G -type main sequence star based on its spectral class. It formed approximately 4.6 billion years ago along with the planets and the moons and the asteroid belt.
The Sun’s core fuses about 600 million tons of hydrogen into helium every second, converting 4 million tons of matter into energy every second as a result. This energy, which can take between 10000 years to 150000 years to escape the core, is the source of the Sun’s light and heat. When hydrogen fusion in its core has diminished to the point at which the Sun is no longer in hydrostatic equilibrium, its core will undergo a marked increase in density and temperature while its outer layers expand, eventually transforming the Sun into a red giant. It is calculated that the Sun will become sufficiently large to engulf the current orbits of Mercury and Venus, and render Earth uninhabitable – but not for about five billion years.
After this, it will shed its outer layers and become a dense type of cooling star known as a white dwarf, and no longer produce energy by fusion, but still glow and give off heat from its previous fusion.
Location of Sun in our own Galaxy
Our Sun and the entire Solar system is located in the galaxy we named as the Milky way. In the milky way the Sun lies close to the inner rim of the Milky Way’s Orion Arm, in the local interstellar cloud or the Gould belt, at a distance of 7.5 to 8.5 kiloparsecs from the galactic centre. The Sun is contained within the local bubble, a space of rarefied hot gas, possibly produced by supernova remnant Geminga or multiple supernovae in subgroup B1 of the Pleiades moving group as shown in the figure below..