White light (what we call visible or optical light) can be split up into its constituent colors easily and with a familiar result – the rainbow. All we have to do is use a slit to focus a narrow beam of the light at a prism. This set-up is actually a basic spectrometer.
The resultant rainbow is really a continous spectrum that shows us the different energies light (from red to blue) present in visible light. But the electromagnetic spectrum encompasses more than just visible light – it covers all energies of light extending from low-energy radio waves, to microwaves, to infrared, to optical light, to ultraviolet, to very high-energy X-rays and gamma rays.
On the next few pages, we'll go into more detail about line and continuum emission – what mechanisms cause them, and what they can tell us about the light-emitting object. But first, to understand the ways in which energy is converted into light, we have to understand how the atom works.
