Red giant Sun and future Earth. Illustration of the Sun, around five billion years in the future, heating a dying Earth. This stage of the Sun's life, known as its red giant stage, will begin when the Sun exhausts the hydrogen fuel in its core. It will then begin burning hydrogen in a shell surrounding the core, and this will cause the Sun to expand. The expanding Sun will engulf the inner planets, and possibly the Earth. If the Earth survives this stage of the death of the Sun, it will freeze as the Sun collapses into a white dwarf star. Image from the ESO Supernova planetarium show 'The Sun, Our Living Star'.