Page 10 - Curriculum Visions Dynamic Book

The life and death of the Sun
The Danish astronomer Ejnar Hertzsprung and the U.S. astronomer Henry Norris Russell both developed charts that can be used to show the life of a star such as the Sun.
The chart on page 11 plots temperature against brightness (luminosity) for the life cycle of the Sun.
Following the diagram around from point A shows the changes that might occur with our Sun.
Nuclear fusion begins at point A. This is the birth of the Sun. The Sun then enters a long period as a yellow main- sequence star, during which time it gets slightly brighter. This stage may last for the best part of 10 billion years, the majority of the life of the star. Since the Sun is 4.5 billion years old, it
is currently about halfway between points A and B. The Sun’s surface temperature is about 6,000°C.
When the hydrogen in the core of the Sun has been used up, fusion in the shell around the core will begin. The Sun will increase in size to nearly half as big again as it is now. This is point C. The Sun won’t have gotten any hotter; but because it is burning hydrogen in its shell and not in its core, it will be about twice as bright as it is now. It will be beginning its red giant phase.
Perhaps 1 to 2 billion years after point C has been reached, the Sun will have grown to over three times its current size and will have reached point D. But it will start to get slightly cooler, and its surface temperature will be about 4,300°C. At this point the Sun will be a huge orange-red disk as seen from Earth.
The increased radiation from the Sun will have increased the temperature of the Earth by 100°C, evaporating all of the oceans and destroying all life.
The Sun will then begin to grow quickly, swelling to a
size that may reach as far as the Earth. At first it will seem as though the Sun fills half the sky. This huge Sun will melt the surface of the Earth, which will return to being covered in molten rock (as it was when the Solar System formed). Then it will fill the entire sky, vaporizing first the planet Mercury, then the planet Venus, and then the Earth. We have reached point E, and the inner rocky planets such as the Earth will be
black dwarf A degenerate star that has cooled so that it is now not visible.
evaporate The change in state from liquid to a gas.
fusion The joining of atomic nuclei to form heavier nuclei.
molten Liquid, suggesting that it has changed from a solid.
planetary nebula A compact ring or oval nebula that is made of material thrown out of a hot star.
radiation The transfer of energy in the form of waves (such as light and heat) or particles (such as from radioactive decay of a material).
red giant A cool, large, bright star at least 25 times the diameter of our Sun.
solar wind The flow of tiny charged particles (called plasma) outward from the Sun.
white dwarf Any star originally of low mass that has reached the end of its life.
 The red giant phase that the Sun might go through (as shown by the Butterfly Nebula).
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