The Life of Our Sun

Imagine you were an alien from a planet where beings were very different to us. Could you put these photos in the right order?

pics   Barrysclipart.com

Astronomers have observed thousands of stars and have figured out that what they are seeing is a life cycle, just like that above. Stars are born, they grow old and then die.

A good starting point is to plot a graph of the luminosity of different classes (essentially temperatures) of star. By examining the light coming from a star (its spectra) we can determine what class of star it is and where it fits on the diagram below.

This is called a Hertzsprung Russell diagram.

You should be able to sketch the main features of this very important diagram including labelling the axes. (notice they are logarithmic, not linear)

Clearly there are several patterns here. Different types of star fall into different groups. Most stars, like our Sun at the moment, fall into the group called the Main Sequence. Though in the future it will probably become a red giant and then a white dwarf. The evolution of a star depends greatly on its mass.

Important - Our Sun is in The Main Sequence at this time. At other points in its life it will not be.

Our Sun's life cycle 1. The Sun evolves from a cloud of gas. Gravity pulls it together. Pressure and temperature increase. 2. A protostar. A ball of super hot gas. Contraction continues. 3. Fusion starts in the core. The star joins the main sequence. Our Sun will be on it for about 10 billion years. 4. Hydrogen in the core begins to run out. Hydrogen in the outer layers starts to fuse causing expansion. The star becomes a red giant. 5. The outer layers are ejected into space forming a planetary nebula. We are left with a very dense, hot white dwarf.

Eventually the white dwarf will cool to become a black dwarf although, at the time of writing this, the Universe is not old enough for any black dwarfs to exist.