A star's surface temperature can be determined by studying the peak wavelength of radiation it emits. Describe how astronomers use the electromagnetic spectrum to determine the surface temperature of a star, and explain why stars of different temperatures appear to be different colours.

Astronomers observe the light from a star with a spectrograph, which spreads the light into its component wavelengths across the electromagnetic spectrum. The spectrum shows a continuous distribution of intensity, with a maximum at a particular wavelength – the peak wavelength. By measuring this peak wavelength, astronomers can use Wien’s displacement law (λ_max = b/T) to calculate the star’s surface temperature.

The peak wavelength shifts to shorter values as the temperature rises. Consequently, hot stars have their peak in the blue or ultraviolet part of the spectrum, making them appear blue or white to the eye. Cooler stars have their peak in the red or infrared region, so they appear red or orange.