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Spectroscopic parallax is the determination of the distance to a star through spectrography. Like parallax, it offers a means to determine the distance to a star, but the word "parallax" is otherwise unrelated and misleading regarding the method, which is as follows: from a main sequence star's spectrum, its spectral type can be determined, and its absolute magnitude can be estimated. The distance is derived by comparing this to its apparent magnitude. Spectroscopic parallax yields an estimate but there are factors that confound the result: reddening and the differences in absolute magnitude due to stellar factors other than spectral type: age, rotation, composition at time of star formation, binary companions, etc. It is more useful in studies of multiple stars (e.g., stellar demographics) than in producing a useful estimate for an individual star.
The term photometric parallax refers to analogously determining the distance to a main sequence star using the absolute magnitude suggested by the star's color indices, which corresponds fairly well to the star's spectral type. This is of use with large photometric surveys.
The term spectroscopic parallax is sometimes used for the latter case, i.e., based upon a color index. Similarly, a spectral type may be cited for a star based upon a color index, e.g., if spectrography has not been carried out on the star. (Photometry is much more efficient and carried out on many more stars than is spectrography.)