• Subclassifications in spectral classes?

    In the spectral classification of stars, there are the major classes--OBAFGKM in the old HKK system--which are subdivided into subclasses, O5, G2, G1, K2, M4. What I seek is the relationship used to compute these subclasses. What formula lets an astronomer say a star is G2 verses G3 or G5?
    In the spectral classification of stars, there are the major classes--OBAFGKM in the old HKK system--which are subdivided into subclasses, O5, G2, G1, K2, M4. What I seek is the relationship used to compute these subclasses. What formula lets an astronomer say a star is G2 verses G3 or G5?
    5 answers · Astronomy & Space · 1 decade ago