Spectroscopic parallax

Spectroscopic parallax or main sequence fitting is an astronomical method for measuring the distances to stars. 
Despite its name, it does not rely on the geometric <a href="/facts/Parallax/Gu8W21LP">parallax</a> effect. The spectroscopic parallax technique can be applied to any <a href="/facts/Main_sequence/DJ3Wq8kd">main sequence</a> star for which a <a href="/facts/Astronomical_spectroscopy/NDGQ7mmM">spectrum</a> 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 10,000 <a href="/facts/Parsec/SwSsk57J">parsecs</a>.
To apply this method, one must measure the <a href="/facts/Apparent_magnitude/7pCTF1Me">apparent magnitude</a> of the star and know the <a href="/facts/Spectral_classification/dYrIuK9H">spectral type</a> 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 its <a href="/facts/Luminosity_class/dYrIuK9H">luminosity class</a>, the spectral type of the star provides a good estimate of the star's <a href="/facts/Absolute_magnitude/R8RVxkLx">absolute magnitude</a>. Knowing the apparent magnitude (m) and absolute magnitude (M) of the star, one can calculate the distance (d, in parsecs) of the star using 
 
 
 
 m
 −
 M
 =
 5
 log
 ⁡
 (
 d
 
 /
 
 10
 )
 
 
 {\displaystyle m-M=5\log(d/10)}
 
 (see <a href="/facts/Distance_modulus/5Wt7RR4s">distance modulus</a>). The true distance to the star may be different than the one calculated due to <a href="/facts/Interstellar_extinction/rLNLDfe1">interstellar extinction</a>.
The method ultimately derives from the spectroscopic studies of sunspots and stars by <a href="/facts/Walter_Sydney_Adams/zYg55xzy">Walter Sydney Adams</a> and <a href="/facts/Ernst_Arnold_Kohlsch%25C3%25BCtter/L3rgta8a">Ernst Arnold Kohlschütter</a>.
The method is an important step on the <a href="/facts/Cosmic_distance_ladder/Xae3hVvK">cosmic distance ladder</a>.

Spectroscopic parallax open-in-new

Spectroscopic parallax