Astronomers analyse the light from distant stars to find out about their properties. Explain how the light from a star can be used to determine its temperature and its chemical composition.

Stars emit a continuous spectrum of light.

The wavelength at which the spectrum is brightest (the peak wavelength) is related to the star’s temperature by Wien’s law. A hotter star has a peak at a shorter wavelength, i.e. towards the blue end of the spectrum, whereas a cooler star peaks at a longer wavelength, towards the red end.

In the continuous spectrum dark absorption lines are seen. Each chemical element absorbs light at specific wavelengths, producing a characteristic pattern of lines. By comparing the observed pattern with known laboratory spectra, the elements present in the star’s atmosphere can be identified, giving its chemical composition.