The electromagnetic spectrum (also called the EM-band) contains gamma rays, radio waves and everything in between. The history of discovering the electromagnetic spectrum is a fascinating one. Sir Isaac Newton used a prism to split sunlight into its fundamental colors of the rainbow.

Sir William Herschel discovered, by accident, the infrared portion of the spectrum when he placed thermometers above the red portion of a projected spectrum. The image on the left shows how this was confirmed, with one of the three thermometers places above the red portion of the spectrum

Johann Ritter suspected "invisible" light on the opposite (blue) end of a spectrum and used paper soaked with silver chloride to detect it. Thomas Young confirmed the wave nature of light (that light moves like waves similar to ocean waves) by examining diffraction patterns through slits.

Michael Faraday and James Maxwell collaborated together to theorize the electromagnetic nature of light - that is changing the electric current in the wave alters its magnetic field. The image below (don't laugh, I'm still learning Adobe Illustrator!) demonstrates how the magnetic portion of this wave is 90^o to the electric portion of the wave - hence 'electromagnetic.'

Experimenting with "Maxwellian Waves," Heinrich Hertz discovered radio waves. Wilhelm Rontgen discovered X-Rays while seemingly serendipitously experimenting with electric current through cardboard tubes with exposed film he had on the other end of the room - he saw the bones of his hand.

It wasn't until Albert Einstein, winning the Nobel Prize for discovering the photoelectric effect, that the wave-particle duality of electromagnetic waves was understood.

Eventually, a tool was created in the form of the electromagnetic spectrum.

As a starting point for understanding the spectrum, visible light covers only a small part - 400 nanometers (blue) to 700 nanometers (red).

The image below is a graph from the Chandra website demonstrating the entire electro-magnetic spectrum. Notice that only a very small portion of this spectrum (in the middle) is made up of visible light.

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