How old is the Sun? Actually it's middle-aged. It was formed about 4,500,000,000 (four and a half billion) years ago and we expect it to carry on pretty much as it is now for a few billion years yet - so no surprises in our lifetimes!
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.
The Sun will grow old in much the same way as humans do. In a few billion years time it will be unrecognisable as the Sun we know today- a bit like the difference between an 80-year old person and a photograph of them as a baby!
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.
Calculations show that, as the hydrogen fuel in the core is used up, the outer parts of the Sun will begin to expand. The Sun will turn from a 'yellow dwarf ' into a 'red giant'. And it really means 'giant'! It will grow so big that it will almost engulf the Earth in its orbit. The outer atmosphere will eventually be puffed out in a gentle explosion and the Sun will be at the centre of a planetary nebula - just like this. , or maybe like the one below. Can you see the old star in the middle of that nebula?
After forming a planetary nebula, the Sun will settle down to old age and quietly cool off for ever and ever and ever….