When studying light, students need to learn that visible light can be refracted into its different wavelengths.  Of course it's ROYGBIV (red, orange, yellow, green, blue, indigo, and violet).  A simple prism is usually used to do this, but I think there is a better way.  Fill up a fish tank with water, put it in the sun, use a mirror and ta da a spectrum!  Check out the video.