There are some basic issues that drive Astronomy and goad astronomers to strive harder. These issues are not difficult to enumerate but are extremely difficult to describe. The simplest way to understand the motivation for astronomical endeavor is to go out on a dark clear night, in a place which isn't flooded by artificial light and look up. The first thing which strikes anyone engaged in this activity is the immensity of what you observe. Equally powerful is the sense of beauty in what you observe. Both these perceptions have been elevated by people into principles which most adhere to very faithfully. Let us consider them individually in some detail.
Greek understanding of the solar system held sway over European astronomy up until Copernicus voiced dissent around 1510 AD. Our understanding of Greek astronomy is based on a book by Ptolemy, an astronomer (and geographer) working in Alexandria. The book was intended as an encyclopedia of Greek thought on the subject. The solar system, in that view, is more properly described as an terrestrial system. The Earth was supposed to be at the center (actually though static it was off center) with the other objects in the solar system in orbit around it. And the stars fixed on the celestial sphere outside the solar system. One thing to note is that, ``... Greek astronomy derived its character from a comment ascribed to Plato, in the 4th century BC, who is reported to have instructed the astronomers to save the phenomena in terms of uniform circular motion. That is to say, he urged them to develop predictive and accurate theories using only combinations of uniform circular motion. As a result, Greek astronomers never regarded their geometric models as true or as being physical descriptions of the machinery of the heavens. They regarded them simply as tools for predicting planetary positions''. This however was not true subsequently in European science. The Ptolemaic ``tool'' was taken to be the ``physical descriptions of the machinery of the heavens''. This helped elevate the Earth to a position of great significance and importance and consequently humans, as kings of the planet, could assert their pre-eminence in the Universe. We were assured of God's attention because we were, literally, the center of the Universe. In one beautiful stroke of genius Copernicus dismantled this grotesque self-aggrandizement of humans. Because the Earth was no longer the center of the Universe the phenomenon of objects falling required explanations other than it was the natural place for everything to be in. This helped lead to Newtonian Gravity. He also made the Universe substantially bigger as will be explained later. But most importantly he changed the mindset of people. Instead of granting Earth the most privileged of all seats in the Universe we recognized ourselves to be one of the many other objects that make it up. This has lead to the almost universal acceptance of the Copernican Principle, that asserts that nothing about us should be expected to be special or unique, as a working hypothesis. When you recognize the degree of change this position entails from the Pre-Copernican European view of humans and Earth it becomes clear why we call it the Copernican Revolution. But, it seems to me to a large part its success in taking hold of our imaginations stems from the overwhelming sense of participation in an unimaginably larger whole that overcomes us whenever we do look up at the sky.
The Copernican revolution did more than displace us from our self-appointed pedestal of pre-eminence. It also simplified our picture of the Universe. Instead of a complex set of epicycles and offset circles we ended up with Newton's gravitation, returning in a full circle to the harmony of the spheres. Although the planets move in ellipses around the Sun, the force which constrains them to move in their orbits is constant in spheres about Sun. The original Greek vision of order and symmetry is restored. This was also such a powerful change that this to has been raised to the level of a principle. Of two theories explaining the same set of phenomena, the one that is simpler and more elegant (in the sense of requiring fewer a-priori axioms and arbitrary parameters to be fixed by a-posteriori observations) is accepted as the better theory. Of course the theory now has to live out its dangerous life by making predictions about phenomena not yet observed and these must be confirmed. But fortunately for us, it appears that Nature disdains the Baroque, at least in as much as the natural ordering of phenomena goes. And this too is part of the Copernican revolution. For part of the principle is the assertion that because Nature is simple and elegant, we can understand it. Which again was an assertion very much akin to the others made during the Renaissance.
One point which needs to be made I think is that Copernican revolution didn't reduce or degrade human stature in the Universe but more put it into perspective and in some ways raised it. Before it, we may have been in the center of Universe but we were ignorant children, unable to think for ourselves, privileged perhaps, but forever condemned to be blind to our role, our destiny in the Universe. Since the Copernican revolution we have exchanged our roles as privileged children with little control or understanding of our destiny to growing adults with less of a sense of being at the center of attention but a greater awareness of the whole.