what is the Sun made of?

Helium was first discovered by observing the spectrum of the Sun. Only much later was it found on Earth. The discovery of helium in the Sun was made by Sir Norman Lockyer and other astronomers during a total eclipse.

The tiny amounts of the other elements such as oxygen, carbon, nitrogen, magnesium and iron in the Sun may at first seem unimportant, but they are in fact very important because it is those elements which give us the clues we need to find out what conditions in the solar atmosphere are like.

Where did those extra elements come from?

They were made in the centres of stars that lived long ago in our galaxy. When stars have used up a lot of their hydrogen and turned it into helium, they get desperate for ways to produce more energy and start to use the helium and turn it into carbon and then into oxygen and so on. If the star is massive enough it can explode towards the end of its life as a supernova. This explosion spreads all those new elements out into space. So when the next generation of stars, like the Sun, is born, the raw material is already 'contaminated' with these important elements.