In the 5th century BC, Plato wrote what has come to be known as his "Allegory of the Cave". In it, he has you imagine prisoners deep inside a cave, who have been chained since childhood. Not only are their limbs immobilized by the chains, their heads are chained as well, so that their eyes are fixed on the wall in front of them. All they can see are the shadows cast upon the wall from their keepers moving around behind them. It is all they know of the world and this two dimensional projection becomes their reality.
In amateur astronomy, it's easy to become trapped in our own version of Plato's Cave. Although we know better, it's hard to escape the illusion that the night sky is a two dimensional celestial sphere. We are aware that the deep sky objects we view are at different distances from us, but we have little idea of how they are positioned in three dimensional space relative to the Earth and the rest of the Galaxy. Many observing guides reinforce this view by focusing on how an object appears to us as we view it in the night sky. The facts most often discussed are the object's apparent data such as its shape, visual magnitude and angular size. The three dimensional positioning and physical properties of the object tends to be ignored.
Why has this seemingly important aspect of our hobby been neglected? First, it is only in the past couple of decades that accurate data on the distance to many deep sky objects has become available. Second, the three dimensional structure of the Galaxy is only now being determined with any degree of certainty, thanks in part to orbiting observatories like the Spitzer Space Telescope. Third, visualizing this data requires a powerful personal computer to be available as an integral part of the analysis.
We are now at a point where all three of these requirements are coming together. Our Galaxy represents an important step in uniting this information to enhance our three dimensional perspective. Amateur astronomy is finally poised to escape from Plato's Cave.
Bill Tschumy
Otherwise