Question: How does colour work?

Sam Geen answered on 21 Jun 2013:

Colour is the frequency of light (or wavelength if you like, the speed of light, which is the same for all light, is just wavelength times frequency). Blue light has a higher frequency than red light. The eye has detectors that pick up light of certain frequencies. These are called cones and rods. The cones work better in bright light and the rods better in dim light. There are three types of cones but only one type of rod, which is why everything looks grey at night – there’s only one “colour” of rod. Look at this graph: http://commons.wikimedia.org/wiki/File:Cone-response.svg. It shows how sensitive the eye is to different frequencies of light. One cone sees blue, one cone sees red/yellow and one sees green. The brain interprets these as colours, and a mixture of frequencies can create different colours.

Telescopes work in pretty much the same way – the instruments in the telescope are like the retina in the eye, and pick up light according to how sensitive the instrument is to different frequencies of light. The difference is that telescope instruments can see frequencies that we can’t – infra red, ultraviolet, even radio waves and x-rays!