What is spectroscopic parallax?
Spectroscopic parallax is the way in which the distance to the stars are measured.
As we know the stars as viewed from the earth are not seen as in their actual position due to atmospheric refraction.But in this method we calculate the distance to the stars by their actual position and the main sequence where its spectrum formation takes place.
The spectrum of the star in order to measure should be very bright.
But apart from this measurement the Trigonometric parallax method is more accurate.
In order to measure the distance to the star using this method,
=> Know the Magnitude of the star (apparent)(denoted as "m")
=>Know the spectral type
=>Knowing the absolute magnitude (denoted as "M")
Now the distance can be calculated as,
where d= distance to the star.