Stellar classification

Stellar classification organizes stars into categories using observable properties, especially spectral features, surface temperature, and luminosity.

Harvard spectral classification: A stellar taxonomy that orders stars by spectral features associated chiefly with surface temperature. Its OBAFGKM sequence supplies the temperature axis used in standard classifications.
Stellar absorption line: A dark feature in a stellar spectrum produced when atoms or ions absorb specific wavelengths. Line strengths and patterns provide the observations used to assign spectral subtypes.
Annie Jump Cannon: An American astronomer who organized stellar spectra and established the OBAFGKM sequence. Her cataloging work made the spectral sequence a practical standard for classifying stars.
Stellar evolution: The sequence of physical changes a star undergoes during its lifetime. A star’s spectral type and luminosity locate it among evolutionary stages.
Yerkes spectral classification: A scheme classifying stars by luminosity-sensitive spectral features, especially in the Morgan–Keenan system. It emphasizes luminosity classes, unlike temperature-only spectral sequences.
Morgan–Keenan classification: A system combining stellar spectral types with luminosity classes, commonly written as a Roman numeral. It extends spectral typing by distinguishing stars with similar spectra but different luminosities.
Blackbody radiation: Electromagnetic radiation with a spectrum determined by an object's temperature. Its temperature-dependent color explains the broad trend behind stellar spectral ordering.
Antonia Maury: An American astronomer whose stellar catalog introduced spectral subdivisions sensitive to line widths. Her luminosity-sensitive observations helped anticipate later distinctions among stellar classes.
Spectroscopic parallax: A distance-estimation method using a star’s spectrum, inferred luminosity, and apparent brightness. Classification supplies a luminosity estimate that can be compared with observed brightness.
Stellar color index: A numerical measure of a star’s brightness difference through two specified wavelength filters. Color estimates temperature but is an observed photometric measure, not a full spectral classification.

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