Spectra and temperature

A star is a good approximation of a perfect black body, an object that emits all wavelengths of electromagnetic radiaton. The wavelength of greatest intensity is determined by Wien's displacement law, which states that peak wavelength is inversely proportional to the absolute temperature of the body.


  • \(\lambda_{\textrm{max}}\) is the wavelength of maximum intensity
  • \(T\) is the absolute temperature
  • \(2.9 \times10^{-3}\) mK is a constant

Spectra and chemical composition

There are three types of spectrum:

  • continuous spectrum shows the full range of visible light wavelengths without interruption. This is emitted by the core of a star.
  • An emission spectrum shows the distinct wavelengths of light released by types of atom. These correspond to the energy changes when an electron moves down in energy level. These become a reference for which to identify the chemical composition that a star is made from.
  • An absorption spectrum shows the continuous spectrum except for those wavelengths absorbed by electrons moving up in energy level in the cooler gases on the outside of the star. By matching these to the emission spectrum, we can determine a star's chemical composition.