I assume you are aware of the different lights known.
Light and its partners can be manipulated in a variety of ways. The most familiar is reflection, in which light is bounced from a surface, the light coming off at the same angle at which it hits, resulting in your undistorted face looking back at you from a mirror. Radiation travels at c only in a vacuum. When it passes into a substance, it slows and can be bent, a common phenomenon called refraction. The effect is easily seen when looking at something through water. Refraction by a curved lens focuses radiation to create an image. Turned to the sky and attached to a detector, the lens becomes an astronomical telescope. (A curved mirror can create a similar image by reflection.) The speed of an electromagnetic wave in a medium depends on its wavelength. Violet light is slowed in a glass of water significantly more than red light. As a result shorter visual waves refract more than do longer ones. Refracted light is therefore dispersed or spread out into its spectrum, creating a rainbow -- or the spectrum of a star. Spectra can also be created by the interference of light waves, the phenomenon that makes the brightly colored patterns seen reflected from a compact audio disc and the halos often observed next to a bright, partly clouded Moon. stars.astro.illinois.edu/sow/spec... Goodbye
