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A Roman numeral after a spectral type.
Also known as: MK luminosity class, Roman numeral star class
The notation adding a Roman numeral to a spectral class to give the star's luminosity and so its size.
Adds a luminosity class to a spectral type, distinguishing a giant from a dwarf of the same temperature.
Contexts: History
Turns a one-dimensional classification into a two-dimensional one, which is what makes the spectral type sufficient to place a star on a Hertzsprung-Russell diagram.
Contexts: History
A Roman numeral written after the spectral letter and digit, sometimes with a lower-case letter qualifying it.