How do we determine the composition of a star?

The composition of a star can be determined through spectroscopy.

Spectroscopy is the study of the interaction between matter and electromagnetic radiation. By analysing the spectrum of light emitted by a star, astronomers can determine its chemical composition. Each element in the star will absorb and emit light at specific wavelengths, creating a unique spectral signature.

To obtain a star's spectrum, astronomers use a spectrograph to split the light into its component colours. The resulting spectrum is then analysed to identify the absorption and emission lines, which correspond to specific elements. By comparing the observed spectrum to known spectra of elements, astronomers can determine the relative abundance of each element in the star.

In addition to determining the chemical composition of a star, spectroscopy can also provide information about its temperature, density, and velocity. By measuring the Doppler shift of spectral lines, astronomers can determine whether a star is moving towards or away from Earth, and at what speed.

Overall, spectroscopy is a powerful tool for understanding the properties of stars and other celestial objects. By analysing the light they emit, astronomers can learn about their composition, structure, and evolution, helping to deepen our understanding of the universe.