What are stars made of?


This week, my daughter has been thinking about stars: “They’re not just twinkly spots in the sky – they must be made of something,”she says. “But what are they made of? And how did they get up there?”

Stars are bright, shining balls of gas in Space. They are mostly made up of two chemical elements: hydrogen (H) and helium (He).

Inside stars, a huge chemical reaction is taking place. This reaction turns hydrogen into helium and creates lots and lots of energy, which comes out as heat and light. Because the amount of energy stars make is so huge, we are able to see them even though they are millions of miles away in Space.

Different types of stars are grouped together into seven classes: O, B, A, F, G, K and M. They range in colour from blue to white, to yellow to orange, to red. And a star’s colour tells us how hot it is: O stars are the brightest, bluest and hottest; M stars are the dimmest, reddest and coolest. This video tutorial explains the different types of stars and gives a handy way to remember them.

It takes millions of years to make a star. They start out as clouds of dust that slowly gather up more and more dust particles, growing bigger and denser and hotter. Eventually, they get big and hot enough in the middle to start the chemical reaction that turns hydrogen to helium. At this point, they become baby stars (or protostars) but they continue gathering up more matter until they grow into full-size stars.

This short video gives an overview of what stars are made of and how they are formed.

The closest star to Earth is the Sun at the centre of our solar system. It took about 50 million years to grow. It’s in G class and is a kind of star called a ‘yellow dwarf’. The Sun looks yellow to us on Earth because it is close enough for us to see its colour. But you should NEVER look directly at the Sun because it shines so brightly that it can damage your eyes very badly!


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