The future of the Sun (and of the Earth)

In this diagram you can see how the temperature and the luminosity (that's the amount of light radiated, or brightness) changes during the life of the Sun. Astronomers use these types of diagrams a lot, and they are called Herzsprung-Russell diagrams after the two astronomers who invented them.

At point A, the Sun starts nuclear fusion in its core. This can be called the `birth' of the Sun.
At this time, about half of the supply of Hydrogen has been used up. This is the situation right now.
The Hydrogen in the core of the Sun has all been used, and the fusion of hydrogen in a shell around the core starts. This makes the sun swell up: Its radius becomes about 40% larger and its luminosity twice as bright.
One and a half billion years later, the surface of the Sun is 3.3 times the size it is now, and its temperature about 4300 degrees. As seen from earth, the Sun will look like a big orange disk. The problem however is that the temperature on earth has increased by about 100 degrees because of this. So all the seas will have evaporated by that time. It can be seriously doubted if any people would survive to see this spectacle...

Within 250 million years, the Sun will grow 100 times larger than it is now, and 500 times more luminous. From the lava-seas of the then molten earth, the Sun will take up almost half of the sky.
The core temperature of the Sun has risen so high that in one bang, all the rest of the helium will fuse into carbon. By this explosion, probably one third of the solar envelope will be thrown out into space,

What happens after that is not well known at this time. The sun will become brighter, and the outer layers will be blown out into space in the form of a very dense solar wind. This is what is called a planetary nebula, and an example of this is seen to the right.

After that, only a white dwarf remains, with a mass of about half of the mass of the current sun, but with an enormous density of 2 tons per cubic centimeter (imagine compressing a car or two into a thimble.. ). This white dwarf will slowly cool down.
This is the end of the solar system: A black dwarf, with the ashes of the planets circling around it.
But that's a long time from now!!

This `Virtual Trip' was created by Michiel Berger, graduate student in Astronomy at the Astronomical Institute of the University of Amsterdam. Most of the material used was taken from the Internet. Some illustrations have been created with Photoshop.

cover If you would like to read an excellent book about the sun, I can highly recommend Journey from the Center of the Sun.
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