The blazing ball of hot hydrogen that warms our planet and provides energy for life won’t be around forever. But how long will the sun last?
Stars, including the sun, have a clear life cycle – a birth, childhood, adulthood and death.
Stars come in many sizes, temperatures and shades of brightness and color. Scientists give them names such as yellow dwarfs, red giants and pulsars.
Stars are born from wispy clouds of dust and debris floating in the space between other stars. By the attraction of gravity, scattered atoms are drawn together. As the dust gets closer and closer, it forms a star.
Tightly packed atoms create a pressure inside the star ball so high that it starts an atomic reaction. Under this great pressure, groups of four hydrogen atoms fuse together into one helium atom, and it gives off energy.
This energy produces the warmth and brightness of the sunshine that falls on us.
Our sun, a yellow-dwarf star, was formed, and its fires started, about 5 billion years ago.
Stars the size of our sun have enough hydrogen to burn for about 10 billion years. Our sun already has used up half its fuel.
In 5 billion years more, our sun will have converted its hydrogen to helium. It will grow larger but cooler, and it will become a red giant. It will be as big as the orbits of Earth or Mars. (Mercury and Venus, which are closer to the sun than Earth, will be burned up completely.)
Earth will have a larger orbit than it does now, but the red- giant sun will still be hot enough to bake everything on Earth into brick.
Our red-giant sun will begin to burn its helium atoms, and they will fuse into atoms of carbon. After many millions of years, the helium will be completely used up.
The sun will blow part of its carbon remains into space as a powerful wind. The remaining electrons will collapse into a white dwarf, a star as small as Earth but much heavier and brighter.
As the white-dwarf sun cools, it will turn Earth into an icy globe. Since all this will take billions of years, we don’t need to worry about the sun failing in our lifetime. There will be warmth and energy for ages to come.
Virginia Science Standards of Learning: 1.6, 3.9, 3.11, 4.7, 6.2, 6.8, ES-4, ES-13, ES-14
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