Article by Michael Burton, Director of the Armagh Observatory and Planetarium
Our view of the cosmos is biased by the vista that is apparent to our eyes. This is what the view in what we call the optically visible portion of the spectrum. To the unaided eye it is a view of a universe full of stars, together with five planets, one Moon and of course the Sun. When augmented with a telescope, our eyes can then see a universe full of galaxies – giant cities of stars.
Yet this is not a representative view of the universe. It misses many types of astronomical objects. The electromagnetic spectrum stretches from low energy radio waves to extremely high energy gamma rays. Optical light takes up just a tiny portion of this spectrum, from blue light with a wavelength of 0.4 microns, to red light with a wavelength of 0.7 microns. A micron is a millionth of a metre, and to give that some perspective, the typical human hair is about 50 microns thick. So very small!
Schematic diagram showing the electromagnetic spectrum, from the radio bands to gamma rays. Credit: wikipedia.
Evolution has given us eyes responsive to optical light as ...