The spectral classification of stars started with the amount of hydrogen present in their spectra, but a better method now uses the amount of oxygen in the star's spectra.

Question

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The spectral classification of stars is primarily based on their temperature, which affects the absorption lines visible in their spectra, not directly on the amount of a specific element like oxygen. The original classification did start with hydrogen lines but has evolved to consider broader spectral features.

The Spectral Classification of Stars Started with the Amount of Hydrogen