LearnStars & evolutionSome maths
Spectral classification
The sequence O B A F G K M, ordering stars from hottest and bluest to coolest and reddest by the lines in their spectra.
Why it matters
It is the single most useful label a star carries. Class implies temperature, which with luminosity implies size, mass and likely fate.
In practice
The star colours in this site's ambient background come from this sequence, weighted the way the naked-eye sky actually is.
Rests on
- Spectral linesSharp bright or dark features in a spectrum, produced when electrons in atoms jump between fixed energy levels.
- Wien's displacement lawThe wavelength at which a blackbody radiates most strongly is inversely proportional to its temperature.
3 concepts in the full chain back to first principles.