Our electromagnetic wavelength detectors – eyes to you and me – are only sensitised to light in the visible part of the electromagnetic spectrum. Whilst I have a great respect for nature and its ability to even develop the eye, a magnificent piece of equipment, it has extreme limitations for the purposes of astronomy.
The diagram below shows that visible light forms a very small part of the full spectrum of electromagnetic radiation; when we, using our eyes, observe astro-nomical objects we are only seeing a part of what is there because we are only using the visible wave-lengths of the electromagnetic spectrum.
Waves in the electromagnetic spectrum vary in size from very long radio waves the size of buildings, to very short gamma-rays smaller than the size of the nucleus of an atom.
Because of the mathematical relationship between the wavelength, frequency and energy we know that the shorter the wavelength the higher the energy. Radio waves with a long wavelength have a low energy and are safe to the human, they surround us in our daily life, moving along the spectrum we reach the infrared region, with its shorter wavelength and therefore higher
energy. Our eyes cannot detect infrared wavelength but our skin can feel the heat or infrared radiation from a warm body eg a piece of charcoal or coal that has been heated but no longer glows. All bodies with a temperature above absolute zero emit detectable infrared radiation to some extent.
Moving further along the spectrum past the visible light wavelengths we reach the ultra violet region with its ability to burn unprotected skin (sunburn); further along is the X-ray and Gamma ray regions – we really do not want to be here – very short wavelength and therefore very high energy with the potential to permanently damage human tissue.
For centuries man has observed in the visible light wavelengths, about 50 years ago we started to observe in the Radio spectrum eg Jodrell Bank and more recently with the ability to observe from above the earth’s atmosphere we now observe in the infrared, visible, ultra violet, X-ray and Gamma ray wavelengths from space. The earth’s atmosphere, as we all know,
acts as a filter to varying degrees to the differing wavelengths so the ability to observe from above the atmospheric shield provides with a wealth of new observing opportunities.
These new observing opportunities have been seized and are producing results; examples include the Hubble Space Telescope observing in visible and infrared wavelengths; Sptizer observing in the infrared; Chandra observing in the X-ray wavelengths; and GLAST, the recently launched Gamma Ray Large Area Space Telescope. And not to forget our very own Jodrell Bank observing in the radio wavelengths.
All of the above space telescopes have websites where you can view their images.
One particularly good site is Cool Cosmos, The Multi-wavelength Astronomy Gallery where you can view, with explanations, a range of astronomical objects each in various wavelengths.
(Note by MG: 10th May 2013: Original link from article had been superseded in the intervening years with the one shown here)