BRAINCAKESpectral Classes
Stars are grouped into spectral classes by the absorption lines in their spectra. These lines depend mainly on surface temperature. In order of decreasing temperature the classes are O B A F G K M.
• O: blue, 25 000-50 000 K; lines of He+, He and H
• B: blue, 11 000-25 000 K; He and H
• A: blue-white, 7500-11 000 K; H (strongest), ionised metals
• F: white, 6000-7500 K; ionised metals
• G: yellow-white, 5000-6000 K; ionised and neutral metals
• K: orange, 3500-5000 K; neutral metals
• M: red, below 3500 K; neutral atoms and molecules such as TiO (titanium oxide)
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Key terms in this lesson
- absorption line
- A dark line at a specific wavelength in an otherwise continuous spectrum, produced when atoms or ions absorb photons of that wavelength.
More in Astrophysics
- Absolute Magnitude
- Black-Body Radiation
- Wien's Displacement Law
- Stefan's Law
- The Hertzsprung-Russell Diagram
- Evolution of a Star
- Supernovae, Neutron Stars and Black Holes
- The Schwarzschild Radius
All 24 lessons in Astrophysics · All AQA A-level Physics topics