This animation illustrates the motion of Jupiter and Saturn in a geo-centric model to explain the occurance of their conjunctions.
These conjunctions (called the Great Conjunctions) occur approximately once every 20 years, in different segments of the Zodiac. They return to the same segment of the Zodiac approximately every sixty years thus setting up a 60-Year cycle. When returning, they are further shifted by approximately 8 degrees thus resulting in these conjunctions drifting across the entire zodiac over time.
In the graphic below, you can play with the 60-Year Cycle and Conjunction sliders to position the planets at a set of pre-calculated conjunctions.