The Sun is a star at the centre of our Solar System. The Earth and other matter (including other planets, asteroids, comets) orbit the sun. The sun accounts for 99.86% of the entire mass of the solar system and it sits at a distance of 93 million miles from Earth. Considering the scale of the galaxy, this distance is relatively short. It takes just 8 minutes for the light from the sun to reach us so, realistically speaking, when we look up at the sun, we see it as it was eight minutes ago!
109 Earths would fit across the sun's surface and 1.3 million Earth's would fill the sun's interior. The Sun's outer visible layer is called the photosphere and has a temperature of 6,000°C (11,000°F). Solar energy is created deep within the core of the Sun. It is here that the temperature (15,000,000° C; 27,000,000° F).
Energy from the sun (sunlight) supports almost all life on Earth and drives the planet's weather. Pressure is so intense inside the sun (340 billion times Earth's air pressure at sea level) that nuclear reactions take place. This reaction causes four protons or hydrogen nuclei to fuse together to form one alpha particle or helium nucleus. The alpha particle is about .7 percent less massive than the four protons. The difference in mass is expelled as energy and is carried to the surface of the Sun, through a process known as convection, where it is released as light and heat. Energy generated in the Sun's core takes a million years to reach its surface. Every second 700 million tons of hydrogen are converted into helium ashes. In the process 5 million tons of pure energy is released; therefore, as time goes on the Sun is becoming lighter.
The sun continuously emits charged particles (mostly protons and electrons), which are the byproducts of thermonuclear reactions occurring inside the sun. These particles take two to three days to reach the Earth and when they reach the Earth's atmosphere they are deflected to the polar regions. The movement of these particles towards the Earth is called solar wind.
The Sun appears to have been active for 4.6 billion years and has enough fuel to go on for another five billion years or so. At the end of its life, the Sun will start to fuse helium into heavier elements and begin to swell up, ultimately growing so large that it will swallow the Earth. After a billion years as a red giant, it will suddenly collapse into a white dwarf -- the final end product of a star like ours. It may take a trillion years to cool off completely.