Spectroscopic parallax ormain sequence fitting[1] is an astronomical method for measuring the distances to stars.
Despite its name, it does not rely on the geometricparallax effect. The spectroscopic parallax technique can be applied to anymain sequence star for which aspectrum can be recorded. The method depends on the star being sufficiently bright to provide a measurable spectrum, which as of 2013 limits its range to about 10,000parsecs.[2]
To apply this method, one must measure theapparent magnitude of the star and know thespectral type of the star. The spectral type can be determined by observing the star's spectrum. If the star lies on the main sequence, as determined by itsluminosity class, the spectral type of the star provides a good estimate of the star'sabsolute magnitude. Knowing the apparent magnitude (m) and absolute magnitude (M) of the star, one can calculate the distance (d, in parsecs) of the star using (seedistance modulus). The true distance to the star may be different than the one calculated due tointerstellar extinction.[3]
The method ultimately derives from the spectroscopic studies of sunspots and stars byWalter Sydney Adams andErnst Arnold Kohlschütter.[4]
The method is an important step on thecosmic distance ladder.
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