How long will the Sun Last? It will be a long time before the sun begins to burn out, at least 5 billion years. The sun is made of hydrogen and helium and radiates energy by nuclear fusion of the hydrogen into helium.
When that does happen, the sun will get bigger and become a giant red star. It may well become so big that Mercury and Venus will collide with it and cease to exist.
Then the sun will begin to cool, and its light will appear to become more red. It will send to earth 100 times more radiation than it does now. On earth, the oceans will boil away. Our air will escape to outer space.
The earth will look like a piece of charcoal. After a few hundred million years as a “red giant,” the sun will start to become what is called a white dwarf. It will become smaller than the earth and change color to white or blue.
On earth, temperatures will approach absolute zero. It will always be dark, and our moon will be almost invisible.
