luminosity class

A star's luminosity class (or Morgan-Keenan luminosity class or MK luminosity class or MK class) is a classification (star class) of the overall size of a star (as are terms like giant star, supergiant, etc.) which is a major contributor to its luminosity. A description of a star might include its spectral class and Luminosity Class. The general classifications are indicated by Roman numerals:

• I - supergiant.
• II - bright giant.
• III - normal giant star.
• IV - subgiant.
• V - main sequence star (dwarf star).
• VI - subdwarfs.

Additional classification:

• Ia-O - extreme luminous supergiants.
• Ia - luminous supergiants.
• Ib - less luminous supergiants.
• D - white dwarves.