In television advertisements and commercial films, animation allows computer-generated objects or characters to interact with human actors, and generally adds realism, drama, or humor to graphical images. From a mechanical perspective, animation is accomplished simply by showing a viewer still images at a rate fast enough to suggest motion. But determining how this sequence of physical images differ from each other over time introduces a variety of issues beyond the task of generating individual images. Ptolemy and Copernicus Perhaps the single greatest consequence of insight into the geometry of a system in motion was that of Copernicus, whose revolutionary ideas about the solar system can be effectively demonstrated with simple two-dimensional graphics. I considered that I too might well be allowed to try whether sounder demonstrations of the revolutions of the heavenly orbs might be discovered by supposing some motion of the earth.
Planet rotate about in on orbits implied by dashed circles.
One consequence of this model is that from the viewpoint of Earth, all orbiting bodies always move in the same direction across the heavens. While it's difficult to capture this motion in a static illustration, Figure 9 attempts to illustrate it by plotting the position of the orbiting Planet as if its distance from Earth were increasing over time. In the Copernican system, planets still travel continuously and in a single direction through space, but our perspective on them is now biased by the fact that we, on Earth, are now moving too. Further Exploration Figure 10. Heliocentric Planetary Motion Imagine there were no other observable planets or stars.