Emission and Absorption Spectra in Stars

• What are the three types of light spectra?

  Continuous, emission, and absorption spectra

  
• How is a continuous spectrum created?

  When photons of all wavelengths are emitted

  
• What does a continuous spectrum look like?

  A broad range of colours
• What produces a continuous spectrum?

  Hot, dense sources like star cores
• How is an emission spectrum created?

  By photons emitted from excited electrons

  
• What does an emission spectrum look like?

  Discrete wavelengths as coloured lines

  
• What produces an emission spectrum?

  Hot, low-pressure gases like nebulae
• How is an absorption spectrum created?

  When photons are absorbed by cool gas electrons
• What does an absorption spectrum look like?

  Discrete wavelengths as dark lines

  
• What produces an absorption spectrum?

  Light passing through cool, low-pressure gases

  
• What is the relationship between absorption and emission spectra?

  Lines in absorption correspond to emission lines
• How is an absorption spectrum formed with a source and observer?

  By placing absorbing material between them
• What causes stellar spectral lines?

  Interactions between photons and gas atoms
• What happens to photons produced in a star's core?

  They move towards the outer gas layers
• What type of spectrum do photons produced in the core form?

  A continuous spectrum
• What occurs when photons are absorbed by gas atoms?

  They excite and re-emit other photons
• What do unique patterns of spectral lines indicate?

  The presence of specific elements in a star
• How can the chemical composition of a star be investigated?

  Even when extremely distant
• What appears in a star's absorption line spectrum if an element is present?

  A characteristic pattern of spectral lines
• What gases predominantly make up the Sun?

  Hydrogen and helium
• How can the composition of the Sun be verified?

  By comparing emission and absorption spectra
• What does each element produce in terms of spectral lines?

  A unique set corresponding to energy transitions
• Which spectrum was first studied in detail?

  The hydrogen spectrum
• What does the Lyman series converge on?

  The ground state n = 1
• What does the Balmer series converge on?

  The second energy level n = 2
• What does the Ritz-Paschen series converge on?

  The third energy level n = 3
• Which series has the most energy photons?

  The Lyman series with shortest wavelength
• Which series has the least energy photons?

  The Pfund series with longest wavelength
• Which series do you need to remember for this course?

  The Balmer series
• What has the discovery of electron transitions allowed astronomers to do?

  Study the nature and composition of objects
• Which electron transition in hydrogen emits visible light?

  n = 3 to n = 2

  
• Why do hot, dense sources produce continuous spectra?

  Atoms interact closely, emitting all frequencies
• Why do hot, low-pressure gases produce emission spectra?

  Photons are emitted from electron transitions
• Why do hot, dense sources observed through cool gases produce absorption spectra?

  Cold gas absorbs energy at specific values
• What do black lines in a continuous emission spectrum indicate?

  Absorption of particular frequencies of light

  
• What should you pay attention to when identifying a star's chemical composition?

  The spacing between the absorption lines