The spectra of all stars show a continuous spectrum like the solar spectrum, in which dark absorption lines are superimposed. The photosphere (inner layer of the star) emits radiations of all wavelengths, producing a continuous spectrum. On passing through the outer (comparatively cooler) layer of the star, radiations of certain wavelengths are selectively absorbed by this layer. This is the cause behind the dark lines in the star's spectrum. These dark lines are characteristics of the substances present in the outer layer of the star. For measuring the surface temperature of the star, we need to measure the wavelength at which the intensity of emitted radiation is maximum and then using Wien's displacement law, given below lamda_m = T = b where b is the Wien's constant and its experimentally determined value is 2.89 xx 10^(-3) mKThe factor on which the colour of a star depends is