A 25 Year Old Gifts Vintage 1997 Limited Edition 25th Birthday T Shirt – though somewhat indirect and subtle – method used for stars that do not fit into these categories (which is the majority of them, at least in our own galaxy) is as follows: First deduce the likely temperature and size of the star from its dominant colour and the atomic spectra present in its light (temperature is related to colour, and different chemical elements are produced under different conditions of temperature and pressure, which in turn depend on the mass and age of a star). From these we can work out the likely luminosity. From the luminosity we can deduce the stars absolute magnitude  (i.e. how bright it would appear at a standard, fixed distance of 10 parsecs from us). Comparing this with the star’s apparent (i.e observed) magnitude, we can then calculate it’s actual distance from us. To me, this method of deducing a star’s distance from us merely by studying its light, and then doing a few calculations based on thermodynamics, nuclear physics, atomic physics and stellar dynamics, represents one of the most beautiful examples of the power of human ingenuity and careful, deductive reasoning in the history of science.
(25 Year Old Gifts Vintage 1997 Limited Edition 25th Birthday T Shirt)