In the MK system, what luminosity class designation is used for main-sequence stars fusing hydrogen, like the Sun (G2V)?
Answer
Class V (Dwarfs)
The Morgan-Keenan (MK) system utilizes luminosity classes to differentiate stars that might otherwise share the same spectral (temperature) classification. The designation for stars that are actively fusing hydrogen in their core and currently residing on the main sequence is Luminosity Class V, commonly referred to as Dwarfs. Our Sun is classified as G2V, indicating it is a main-sequence yellow dwarf. This class stands in direct contrast to evolved stars like Giants (Class III) or Supergiants (Classes I, II, IV), which have exhausted core hydrogen and are dramatically larger and more luminous despite sometimes sharing similar surface temperatures with a dwarf star.
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