The Suns future

The Sun is about 4.5 billion years old and it is not quite half-way through its lifespan. Throughout the second half of its life, the Sun is expected to increase gradually in size, luminosity and temperature. In about 5 billion years' time, the Sun will have expanded to about three times its present size. As it uses up its hydrogen it will become more orange in colour. By this time, temperatures on Earth will be much higher and all the water will have evaporated. As the Sun continues to expand, reaching about

Figure 3.11 The Hubble Space Telescope recorded this picture of a star, similar to our Sun, exploding and sending out much of its material into space. (Photo: NASA)

100 times its present size, it will become a red giant and engulf Mercury and Venus. Earth will be scorched to a cinder. As hydrogen is used up, the core of the Sun will slowly contract, forcing the Sun's central temperature to increase. When the core temperature reaches 100 million degrees Celsius, helium fusion begins to generate carbon and oxygen. The temperature in the core continues to rise, causing helium to fuse at an increasing rate. An explosion (the helium flash) will result, and a third of the Sun will be blown away. Eventually the Sun will lose its outer layers and contract to become a white dwarf about the size of Earth.

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