The Sun is about 4.57 billion years into its main-sequence stage and when we think of its age, that’s the number generally agreed on. You can think of this as the relatively stable period in a star’s life after it forms and during which it converts Hydrogen into Helium in a process known as nuclear fusion. Scientists estimate our star is about half-way through its main-sequence stage. In a little more than 5 billion years from now and once most of the Hydrogen in its core has been converted, the Sun will enter its next stage of evolution, its red giant stage.
During the Sun’s red giant stage, it will swell in size until it is bigger than the Earth’s orbit. Life will have long since died on Earth before this happens. In fact, the sun is warming more and more even now. Some estimates hold that life will be impossible on Earth due to solar heat in less than 1 billion years! Don’t worry, though, that’s plenty time for us all to move a little further out to Mars and maybe even to other stars! While in its red giant stage, the super-hot core of our star will burn Helium and convert it into Carbon.
After its red giant stage, the sun will begin to cast off its outer layers in a spectacular show, forming what’s known as a planetary nebula. The picture to the left was taken by the Hubble Space Telescope and shows a planetary nebula designated NGC 6369: The Little Ghost Nebula.
After completing it’s red giant stage and casting off its outer layers, what will be left will be a white dwarf.