THE SPECTRUM                                           [home]   [topic page]

Most think of the spectrum as red through to violet as in the rainbow. It has been known for a long while that the rainbow is only the VISIBLE part of the spectrum and that invisible parts are also present.

The "light" of the whole spectrum is vast in range and it includes radio waves, infrared radiation, microwaves, ultraviolet waves, X Rays and gamma rays! All travel at the speed of light itself - 300 000 km each second.

The measure of a colour or position on the spectrum is either the frequency, "f" or the wavelength, "l". These are related through the equation

Speed of light = frequency x wavelength.

The Sun emits right through most of the spectrum. It is most powerful in the yellow/green part which coincides with the most sensitive part of the human eye's performance. It is also a powerful emitter in the infrared.

Nonreptiles such as mammals and birds are strong emitters in the infrared but are not emitters in the visible. We cannot see each other in the dark, so no visible light is emitted from us - but when we put our hands near our faces, we can feel the radiation from them. Our skin is sensitive to infrared radiation. "Infrared detectors" which change their properties when IR lands on them can "see" sources of IR. Humans can be detected easily in the dark with these detectors so they are very valuable to search and rescue helicopters and the military.

Infrared picture of a hand and a handprint on a piece of paper in a ringlock folder. The paper has been warmed by the hand and emits more radiation than its cooler surrounds. Obviously this scene is invisible to the naked eye. ( http://repentium.gsfc.nasa.gov/~dsb/718firo.html )