Short answers, pulled from the story.
The Sun is the star at the centre of the Solar System, a massive sphere of hot plasma heated to incandescence by nuclear fusion in its core. It makes up about 99.86% of the total mass of the Solar System and sits about 8 light-minutes from Earth.
The Sun formed approximately 4.6 billion years ago from the gravitational collapse of part of a giant molecular cloud of mostly hydrogen and helium. The age is consistent with the radiometric date of the oldest Solar System material at 4.567 billion years, and the collapse was likely triggered by a shock wave from a nearby supernova.
Every second the Sun's core fuses about 600 billion kilograms of hydrogen into helium and converts about 4 billion kilograms of matter into energy. This equals 384.6 yottawatts, or about 9.192 megatons of TNT per second.
The corona reaches about 1,000,000 kelvin while the photosphere sits near 6,000 kelvin, so it cannot be heated by direct conduction from the surface. Two mechanisms are proposed, wave heating from convection-zone turbulence and magnetic heating through magnetic reconnection, with research now focused on flare heating.
In about 5 billion years core hydrogen fusion will stop, and the Sun will expand into a red giant that engulfs Mercury, Venus, and eventually Earth at 7.59 billion years from now. It will then shed its outer layers as a planetary nebula and become a white dwarf containing an estimated 54.05% of its present mass.
Giovanni Domenico Cassini determined the first reasonably accurate distance in 1684 by measuring the parallax of Mars. He sent Jean Richer to Cayenne for simultaneous readings, observed from Paris, and applied Kepler's laws, arriving at a value about 10% smaller than modern figures.
The Sun consists mainly of hydrogen and helium, which account for about 74.9% and 23.8% respectively of the photosphere's mass. Heavier elements make up less than 2%, with oxygen, carbon, neon, and iron being the most abundant.