Stars - Luminosity Classes

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Stars - Luminosity Classes

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STARS - LUMINOSITY CLASSES (MK SYSTEM)

CLASS   STAR TYPE

O¹      Extremely luminous hypergiants, so far seen only in the Magellanic Clouds and the Galaxy.

Ia      Luminous supergiants.

Ib      Lower luminosity supergiants.

II      Bright giants.

III     Ordinary giants.

IV      Subgiants.

V       Dwarfs (mostly main-sequence stars).

VI²     Subdwarfs.

VII²    White dwarfs.

Notes: ¹ Arabic O, not Roman, now a standard letter but added to the system later.
² Not a standard part of the MK system but often used anyway.