3.2 The Electromagnetic Spectrum: Beyond Visible Light text pp 96-100

Visible light is just one small part of the electromagnetic spectrum. This galaxy has been photographed using light waves in the x-ray section of the EM spectrum.

The difference between one kind of electromagnetic energy and another is the length of their waves, or their wavelengths. Gamma ray burst

Wavelengths can run from 10-18 meters or less to wavelengths thousands of kms long. The Crab Nebula

This image of the Crab Nebula combines visible light (green, from the Hubble Space Telescope), radio waves (red, from the National Radio Astronomy Observatory) and x-ray (blue, from the Chandra Observatory). (Image credit: NASA/CXC/ASU/J. Hester et al, NASA/HST/ASU and NRAO/AUI/NSF) This image of the Crab Nebula combines visible light (green, from the Hubble Space Telescope), radio waves (red, from the National Radio Astronomy Observatory) and x-ray (blue, from the Chandra Observatory). (Image credit: NASA/CXC/ASU/J. Hester et al, NASA/HST/ASU and NRAO/AUI/NSF)

The Exploration of the EM spectrum began in 1800, when Sir William Herschel showed that heat radiation was related to visible light. He named this energy infrared.

In 1801, J. Ritter discovered ultraviolet radiation while experimenting with chemicals that might be sensitive to light. Silver Chloride (used in photography) darkened most strongly in the region just beyond the violet end of the spectrum.

The existence of radio waves was predicted in the mid-1800s, but it was 20 years before Heinrich Hertz produced them in 1888.

It was another 50 years before Karl Jansky discovered naturally occurring radio waves from cosmic sources, including the center of the Milky Way.