The burning core of a star gives off light and other energy in a spectrum of wavelengths. We can observe these different wavelengths of light as a band of colours...like a rainbow. The colours indicate what chemical elements are in the hot core of the star, giving off light. The light from the core of the star must pass through the relatively cooler outer layers of the star before heading off into space. These cooler gases absorb some of the light, creating black bands in the rainbow spectrum we eventually see. These bands correspond directly with elements (such as hydrogen) present in the outer layers of the star. In addition, if the star is moving towards or away from us at a measureable fraction of the speed of light, this speed will show up in the spectrum as a shift of these dark bands from their normal position, due to the Doppler effect. For objects moving away, the bands shift towards the red end of the spectrum. This effect, called the 'red shift', gave the first evidence that our universe is expanding...all the furthest galaxies show a red shift in their spectra! Back Site Map | Main Page