What concept did observing Jupiter holding four moons in orbit help observers grasp as a universal principle?
Answer
Gravity and orbital mechanics being universal principles
Seeing four distinct objects held in orbit by a distant primary body (Jupiter) showed that gravity and orbital mechanics were universal principles, not forces unique only to the Earth-Moon system.

Related Questions
What astronomical framework, championed by Ptolemy, was the accepted standard for centuries?In what year did Galileo Galilei first turn his telescope skyward and observe the moons of Jupiter?What name did Galileo initially give to the four newly discovered celestial objects orbiting Jupiter?What physical observation directly contradicted the main assertion of the Ptolemaic geocentric system?Galileo’s observations facilitated a fundamental shift in scientific authority away from which sources?How did the heliocentric model explain the existence of Jupiter's moons more economically than the geocentric model?What concept did observing Jupiter holding four moons in orbit help observers grasp as a universal principle?What crucial element did Galileo’s discovery provide that Copernicus’s earlier proposal lacked?What was the critical technological enabler for Galileo's world-changing observation?What further observation, also requiring the telescope, was needed to cement the proof for the heliocentric model?