There is also a method called brightness measurement (simpler explanation of spectroscopic parallax):
There is no direct method currently available to measure the distance to
stars farther than 400 light years from Earth, so astronomers instead
use brightness measurements. It turns out that a star's color spectrum
is a good indication of its actual brightness. The relationship between
color and brightness was proven using the several thousand stars close
enough to earth to have their distances measured directly. Astronomers
can therefore look at a distant star and determine its color spectrum.
From the color, they can determine the star's actual brightness. By
knowing the actual brightness and comparing it to the apparent
brightness seen from Earth (that is, by looking at how dim the star has
become once its light reaches Earth), they can determine the distance to the star.