The Sun, just one of more than 100 billion stars in our galaxy, is the largest object in our solar system. It contains more than 99.8% of the total mass of the solar system (with Jupiter containing most of the rest). The Sun is one of the larger stars in the galaxy.
Currently the Sun consists of about 70% hydrogen, 28% helium and 2% metals. However these figures are slowly changing as the Sun converts hydrogen to helium in its core.
The Sun's energy output is 386 billion billion megawatts and is produced by nuclear fusion. Each second about 700,000,000 tons of hydrogen is converted to about 695,000,000 tons of helium and 3.86e33 ergs of energy as gamma rays. As this energy travels out towards the surface, it is constantly reabsorbed and readmitted at lower and lower temperatures, so by the time it reaches the surface, the energy is mainly visible light.
The Sun is a gas body, so the outer layers of the Sun show differential rotation, that is different parts of the surface rotate around the Sun at different speeds to other parts, for example the area around the equator rotates every 25.4 days, whereas nearer the Sun's poles it is closer to every 36 days. This effect extends far down into the interior of the Sun but the core of the Sun rotates as a solid body.
The core consists of approximately the inner 25% of the Sun's body. It has a temperature of 15.6 million Kelvin (K), a pressure of 250 billion atmospheres and the centre of the core is 150 times denser than water.
The Sun's surface is called the photosphere and it has a temperature of approximately 5800 K. On the surface are sun spots which are the 'cool' regions of the surface at a 'mere' 3800K. The sun spots can be large, with diameters of 50,000 km. They are caused by the Sun's magnetic field which is very strong and extends past Pluto.
Above the photosphere is the chromosphere and above the chromosphere is the corona which extends millions of kilometres into space. The corona can be seen when there is a full solar eclipse. Temperatures in the corona are over 1,000,000 K.
As well as heat and light the Sun also emits a low density stream of charged particles (mostly electrons and protons) called the solar wind.
The Sun is about 4.5 billion years old. It has used up about half of the hydrogen in it's core. The Sun will continue pretty much as it is for another 5 billion years, until it uses up its supply of hydrogen. The Sun will the change into a red giant, the process of which will destroy the Earth. It will remain as a red giant for another billion years and then it will collapse into a white dwarf where it could take up to a trillion years to completely cool down.