Question

What tests would be undertaken to tell what elements are being fused by a star?

E.g. how could anyone tell whether a star is fusing helium or magnesium.

Is it based on the colour of light emitted? If so what would these be for fusion from hydrogen to iron?

Answer 1

We can determine the composition of a star with a 'test' or procedure called spectral analysis. Based on the spectrum, astronomers understand the chemical contents of the star's atmosphere. The absorption spectra for hydrogen to iron can be seen below: