in an absorption spectrum for a cloud of the same element. Elements in the star's outer layers absorb light from the continuous black-body spectrum of the star. A comparison of a star's absorption spectrum with the spectra of known elements allows the chemical composition of the star's outer layers to be deduced. You may be provided with a graph of intensity against wavelength for the spectrum of a star. Analyse the information by first identifying the wavelength at which the black body curve is at its highest intensity. You will need to be able to justify your estimate of this wavelength. This can best be done by drawing a vertical line down from the peak of the curve so that it intercepts the horizontal (wavelength) axis. You may need to interpolate between divisions on the wavelength axis. Take care to ensure that your answer is given in the correct SI unit. In order to predict the surface temperature of the star from the wavelength of maximum intensity, you will probably be given the Wien's Law equation: where (W = 2.89 x 10 -3 m.K). Rearrange the equation so that T is the subject of the equation, then substitute in the value of wavelength from the graph. Example: The intensity/wavelength graph of a star is given below. Use this curve to predict the star's surface temperature. Solution: From the curve the wavelength at which the intensity is a maximum is approximately 5.8 x 10 -7 m. The star's surface temperature is