how old is the Sun?

A star’s life-cycle depends on its mass. Stars like the Sun spend most of their lives quietly eating up the hydrogen in their centre. That means their temperature and size stay very much the same for billions of years.

When the Sun is about 7 billion years old it will slowly start to change and will become bigger and cooler. By the time it is 10 billion years old it will have changed into a red giant and its atmosphere will stretch out to near where the Earth is today.

Under-sea coral? Enchanted castles? Space serpents? These eerie, dark, pillar-like structures are actually columns of hydrogen gas and dust where new stars are being formed. This picture of the Eagle Nebula was taken with the Hubble Space Telescope. The nebula is 7000 light years from Earth and is huge - the largest pillar is about four light years from top to bottom!

The Sun and stars don't seem to change much year after year so how can we know about their lifecycles? One method is to have computer programs to calculate how a star evolves as it uses up its energy resources. Another way is to observe many stars. We see many different kinds of stars and we assume the reason for this is that we are seeing stars at different stages of their lifecycle. We can then begin to build up an explanation of how and when they change.

It's a bit like observing all the people in a town centre. We assume that they are all basically the same kind of animal (human beings) but that the main differences are caused by them being at different stages of their lifecycle (age). Fortunately, we don't have the complication of male and female stars!

When and how will the Sun die?

The Sun will not die in the way we know plants and animals die. But in a few billion years it will have changed so much it will not be recognisable as the Sun we know today.

After forming a planetary nebula, the Sun will settle down to old age and quietly cool off for ever and ever and ever….

what colour is the Sun? | how hot is the Sun? | how bright is the Sun?
how big is the Sun? | what's the mass of the Sun?

what is the Sun made of? | does the Sun rotate?