In the stellar designation K5 III, what status does the Roman numeral 'III' indicate?
Answer
A Giant star that has expanded significantly
The Roman numeral 'III' in a stellar designation like K5 III signifies that the star belongs to the Giant class. Stars achieve this status after evolving off the main sequence, meaning they have ceased core hydrogen fusion and have expanded considerably in physical size. This expansion drastically increases their overall energy output compared to main-sequence stars of similar mass, even if their surface temperature (indicated by K5) has dropped.
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