What specific, erratic planetary behavior forced the geocentric model to adopt complex additions like epicycles?
Answer
Retrograde motion
Planets like Mars, Jupiter, and Saturn periodically appeared to slow down and move backward for a time, a phenomenon known as retrograde motion, which the model struggled to explain simply.

Related Questions
What is the geocentric model often called, named after an influential Greek astronomer?What was the most immediate and compelling strength of the geocentric view?What specific, erratic planetary behavior forced the geocentric model to adopt complex additions like epicycles?What were the small circles, championed by Ptolemy, upon which planets moved while their centers traversed larger paths?Which key observation, later confirmed by Galileo with his telescope, provided powerful evidence against the geocentric structure?The inability to detect which phenomenon led proponents of the geocentric model to logically conclude that the Earth must not be moving?What factor allowed the geocentric model to dominate for over a thousand years despite its mathematical complexities?Philosophically, why was placing humanity at the center of the cosmos appealing to many historical thinkers?In contrast to the geocentric view, what does the heliocentric model explain retrograde motion as?What key scientific virtue did the geocentric model ultimately sacrifice in order to match observational data accurately?