Spectra.- The light from a star or galaxy can be split into its individual colours (or spectrum), just like you see sunlight split into beautiful band of colours by reflection from a crystal glass or in a rainbow. We can study the spectrum of a star or galaxy in a very detailed way using our telescopes, instruments and electronic detectors. These colours change depending on the velocity of the star or galaxy because light is made up of tiny waves. The same effect can be heard in sound waves - when you listen to a car siren coming towards you it has a higher pitch than when it is moving away from you, and is called the Doppler effect (after its discoverer).