The Spectrum of a Star

We have seen how the Fraunhofer spectrum has told us so much about the composition of the Sun. We can gain similar information about the composition of other stars by examining their spectra, i.e. the intensity of the different wavelengths of light they emit.

 Of course we need very sensitive instruments to do this. A machine is used called a spectrograph.

                 
                                                                                                                  Courtesy of J.B. Kaler   University of Arizona     

Light collected by the telescope actually passes through something called a diffraction grating, this does exactly the same job as a prism, splitting the blended light into its different wavelengths. This light falls on electronic sensors, very similar to those inside a digital camera, which measure the wavelength and intensity of the star's spectrum.

Above is the spectrum produced by a certain star.

• The shape of the graph and where the hump is tells us the temperature of the star
• The spikes (absorption lines) tell us what elements it contains

We shall see in the next topic how we can also use this information to calculate how fast the star is moving relative to us.