Stellar Spectral Classes

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Stellar Spectra

A lot can be learned from stellar spectra, such as their temperature and composition.

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Temperature sensitive

  • The temperature of the star has an effect on the absorption of light by atoms.
  • The hydrogen Balmer lines (which occur when the electron drops down to the n = 2 state) are strongly temperature sensitive as shown in the diagram.
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Energy levels

  • Cool stars have very few hydrogen atoms in the n = 2 level and so give weak Balmer lines.
  • Very hot stars have more atoms in the n = 3 level.
  • ‘A’ class stars have the right temperature for most of the electrons to be in the n = 2 level.

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

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