A Map of Visible and Invisible Light

Our understanding of the nature of light took a giant leap forward in the second half of the 1800’s with the help of the Scottish physicist James Clerk Maxwell.

Maxwell was interested in a multitude of scientific problems that included electricity and magnetism. He first published articles on these subjects in 1855, then compiled his work in 1873 into a book entitled Treatise on Electricity and Magnetism, which is now considered a classic in the field of matter.

In 1863, Maxwell discovered that by manipulating equations for electricity and magnetism, it was possible to extract a value that corresponded to the speed of light. Surprised by this result, he began to suspect that light, electricity and magnetism were one and the same.

To follow up on this idea, he developed new equations for electricity and magnetism and concluded that not only is light a wave – as demonstrated by Thomas Young more than 50 years earlier – but an electromagnetic wave. The discovery that light possesses both electric and magnetic components proved to be of paramount importance.

Heinrich Rudolf Hertz.Maxwell went on to reason that invisible electromagnetic waves exist beyond the visible and ultraviolet light spectra, but sadly he did not live long enough to test his idea. Maxwell died in 1879, not long after developing his theory.

The year of 1888 provided the consecration of Maxwell’s work when the German physicist Heinrich Rudolf Hertz succeeded in demonstrating three important facts: that electricity can be transmitted by electromagnetic waves, that these waves travel at the speed of light, and that their wavelengths are a million times the length of visible light and ultraviolet waves.

Hertz labelled these new waves “radio waves”, and their discovery was put to beneficial use in the development of the telegraph and the radio.

The electromagnetic spectrum is continuous but scientists have divided it in an artificial manner for practical reasons. The divisions were mainly established by the limitations of the various techniques used to detect wavelengths. For example, the limits of the visible light range is defined by what our eyes can detect.

Although other electromagnetic waves – radio waves, infrared light, ultraviolet light, X-rays and gamma rays – represent “colours” that are invisible to us, they are nonetheless forms of light.

Follow this link to the electromagnetic spectrum activity.
ASTROLab of Mont-Mégantic National Park

© 2006 An original idea and a realization of the ASTROLab of Mont-Mégantic National Park

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