How do astronomers determine the composition of stars?

Astronomers determine the composition of stars by analysing the light they emit using a technique called spectroscopy.

Spectroscopy is a scientific method that involves studying the interaction between matter and electromagnetic radiation. In the case of stars, astronomers use this technique to examine the light they emit. When a star's light is passed through a prism, it is split into a spectrum of colours, similar to a rainbow. This spectrum contains dark lines, known as absorption lines, which are unique to each element. By identifying these lines, astronomers can determine which elements are present in the star's atmosphere.

The process begins by capturing the star's light using a telescope. This light is then directed through a device called a spectrograph, which splits the light into its constituent colours. The resulting spectrum is recorded and analysed. Each element absorbs light at specific wavelengths, creating a unique pattern of dark lines in the spectrum. These patterns, known as spectral lines, serve as 'fingerprints' that allow astronomers to identify the elements present.

The strength of these spectral lines can also provide information about the abundance of each element. Stronger lines indicate a higher concentration of a particular element. Additionally, the width of the lines can give clues about the pressure in the star's atmosphere, while the overall shape of the spectrum can reveal the star's temperature.

In addition to identifying elements, spectroscopy can also help astronomers determine other properties of stars, such as their temperature, density, and motion. For example, the Doppler effect causes the spectral lines to shift towards the red or blue end of the spectrum depending on whether the star is moving away from or towards us. This can be used to measure the star's velocity and distance.

In summary, by studying the light emitted by stars and analysing the patterns in their spectra, astronomers can determine not only what stars are made of, but also gain valuable insights into their physical properties and behaviour.