Line spectrum

• From Earth, we can figure out the chemical composition of a star by looking at the absorption spectrum that it produces
• A star is a source of light
• Continuous spectrum


  A spectrum made of a continuous range of wavelengths or frequencies
• Emission spectrum


  Bright spectral lines against a dark background
• An emission spectrum can be produced by a hot gas that is emitting photons of particular frequencies
• Absorption spectrum


  The frequencies missing from the continuous spectrum
• Emission spectrum


  Subtracted from continuous spectrum gives absorption spectrum
• Emission and absorption spectra are categorized as line spectra to distinguish them from continuous spectra
• How absorption spectrum is produced

  1. Star emits photons of all frequencies to produce continuous spectrum

  2. Photons get absorbed by cooler gas around star

  3. Gas becomes excited and emits photons giving emission spectrum

  4. Photons that form absorption spectrum are the ones that did not get absorbed by the gas