The essentials about the sun
Beside the sun, the planets and moons of the solar system seem insignificant. The sun accounts for 99.86% of the mass of the solar system. It consists mainly of hydrogen and helium that has been continuously fusing for 4.5 billion years. The size of the sun will change a lot. At the end of life, it will swell like a balloon to encompass Mercury, Venus and the Earth. After its red giant phase, the opposite will happen. Unable to compensate for its own gravity, the sun will collapse into a white dwarf barely larger than the Earth.
Image by NASA/SDO (AIA) [Public domain]