Roberta A. Mazzucco
The Sun will continue as it is now until it consumes about 90% of the hydrogen in its core. It has been calculated by scientists that the whole process for a star the size of our Sun would take about 10 billion years about half of which the Sun has already used up. When the hydrogen in the Sun's core is nearly spent its core will shrink and grow hotter. The rising temperature in the core will make the remaining hydrogen burn faster, producing more energy. This energy will flow outward through the layers of the Sun and lift them and cool them as they move further from the Sun's surface. The Sun will now be bloated and cool. It will turn into a red giant. Cool here is a relative term since the Sun will still give out more than 1000 times the energy of the current Sun even though the surface will be cooler. Anyone then on the Earth will only get a quick look because the expanding Sun will engulf the Earth. (19)
The Sun will shine as a red giant for maybe a billion more years and then will shrink and grow hotter and finally when it gets hot enough it will turn into a yellow giant. During this stage the Sun will start to pulsate as if taking slow deep breaths. As it consumes most of the helium in its core it will turn again into a red giant even larger and brighter than before. That intense brightness will signal its death. All of its energy will be streaming out into space forming a gaseous shell that will eventually disperse. The tiny core will be very hot but with no more fuel. It will cool and shrink into a white dwarf.(20)
