The picture represents a panoramic view of how the sky would appear if our eyes were sensitive to radio waves rather than to light. Such a sight would go a long ways toward persuading astrologers as to the existence of preferential directions in space. While 'bright' discrete radio sources do stand out, the overpowering sense received from such a view is of the shape or body of our galaxy. There is no mistaking the galactic plane and the very heart, the center of the galaxy. It abounds with light. We could renew our sense of cosmic direction almost any night of the year by just walking outside.
Why we cannot see at visual frequencies the great light of the galactic center (GC) is very simple. At visual wavelengths, great clouds of relatively near dust intervene and block our view of the GC and of much of the galactic plane. These dark clouds, in general, prevent us from seeing more than a few kiloparsecs in any direction along the galactic plane. If we could see our galaxy from the vantage point of a neighboring galaxy, such as Andromeda, the center would appear filled with light.
Radio and infrared waves are able to bend around the particles of dust and to reach us. Only in recent years has it been possible to really "see" the actual center and structure of our galaxy. The radio maps of the heavens shown on these pages bring out the basic shape, body, and "aura" of our galaxy. Our dependence upon the EYE and optical frequencies results in an idea of the heavens as filled with an infinite number of points of light or stars, but otherwise relatively empty of form. The stars are 'set' in space, but most of us do not have much sense or feel for the fabric or matrix in which these stars are set. This shape becomes clear in radio maps and it is obvious that the great galaxy is the mother and home of the countless stars within it. Radio maps reveal that whole areas of the sky are filled with more light than others and that this light is graded, with a concentration toward the galactic plane and, of course, the galactic nucleus.
Until about 40 years ago, our knowledge of the cosmos outside the sphere of the Earth came almost entirely from the light we could collect with large mirrors and lenses. In fact "light" meant to us the eye and the visual part of the electromagnetic spectrum. The atmosphere surrounding the Earth is largely opaque (blocks) to most parts of the electromagnetic spectrum, although there are several transparent regions through which we may receive light and thus "look" out into space. These have been termed "windows," and the two most important windows are the optical and radio bands of the light spectrum. If we compare these two windows to the sound spectrum, the radio window represents a ten-octave span, while the optical window represents a little less than a single octave! There are several other bands of relative transparency in the Infrared range through which appear an almost entirely different set of stars and constellations. In fact, the range of energy between the extremes of the electromagnetic spectrum is so great that very different techniques have evolved for their study.
The atmosphere of the Earth serves to shield the Earth from much of the radiation reaching it from outer space, with the exception of the two windows in the visual and radio frequencies. In recent years man has removed the entire concept of windows by bypassing the atmosphere through the means of balloons, rockets, and other space vehicles. Beyond our atmosphere, the entire range of the "light" spectrum is wide open to our reception. In our lifetimes, we have experienced not only a fantastic increase in receptivity of light but have made active outreach beyond the atmosphere and Earth itself. We have stepped beyond ourselves into the space beyond and into ideas outside our imagination but a few years ago.
Copyright (c) 1997-99 Michael Erlewine