Spectroscopic Parallax (3)

NOTE: We’re assuming more distant stars are just like nearby ones!
BUT WAIT! Not all stars lie on the Main Sequence
Subtle differences in the widths of the star’s absorption lines can determine its “Luminosity Class” (WD, MS, giant, supergiant)
Measure spectrum + blackbody + atomic physics => TEMP and LUMINOSITY CLASS
+ CALIBRATED HR DIAGRAM => LUMINOSITY
+ APPARENT BRIGHTNESS + INV SQ => DISTANCE

NOTE: We’re assuming more distant stars are just like nearby ones!