A complete MK designation includes both spectral type and luminosityclass -for instance, the sun is a G2V.
一个完整的MK系统代号包含光谱类型和光度型两部分——例如,太阳属于G 2 V类恒星。
2
In principle, one can trace that history back in cosmic time by observing a so-called standard candle, a class of astronomical object whose intrinsic luminosity is uniform.