Spektraltyp

Spektraltyp is a term used in astronomy to classify stars based on their spectral characteristics, specifically the absorption lines present in their spectra. These lines reveal the chemical composition, temperature, and other physical properties of a star's atmosphere. The most common spectral classification system is the Morgan-Keenan (MK) system, which categorizes stars into spectral types designated by letters: O, B, A, F, G, K, and M.

These letter types are ordered from hottest to coolest. O-type stars are the hottest and bluest, with strong ionized helium lines. B-type stars are also very hot, showing neutral helium and ionized hydrogen lines. A-type stars exhibit the strongest hydrogen lines. F and G stars have progressively weaker hydrogen lines and stronger lines of neutral and ionized metals. G-type stars, like our Sun, are characterized by their prominent G-band of ionized magnesium. K-type stars are cooler and redder, with even stronger metallic lines and molecular bands appearing. M-type stars are the coolest and reddest, dominated by molecular bands, particularly those of titanium oxide.

Each spectral type is further subdivided into numerical subclasses from 0 to 9, with 0 being the hottest and 9 the coolest within that type. For example, G2 is a specific classification within the G spectral type. The MK system also includes luminosity classes, denoted by Roman numerals I through V, which indicate the star's size and evolutionary stage (e.g., I for supergiants, III for giants, V for main-sequence or dwarf stars). Therefore, a star's full spectral type might be represented as G2V for a Sun-like main-sequence star.