Galileo used a telescope to cast his eyes upon Jupiter and its moons Io, Europa, Ganymede, and Callisto in 1610. He recorded notebook drawings of their positions nightly. He believed they moved around the planet Jupiter in what appeared to be orbits. His views were but snapshots in time.
Telescopes improved over time. Technology brought us better views. Spacecraft Voyager and Galileo gave us marvelous images of the moons. But, those detailed images still gave us only snapshots in time. Those amazing views still lacked the perspective needed to show them in actual orbit about Jupiter.
Our view of the moons changed with the arrival of the Juno spacecraft on 4 July 2016. It approached Jupiter from above the plane of the orbits of Jupiter and its moons. The perspective allowed the JunoCam camera onboard to image the system multiple times for 17 days between 12 June and 29 June. The still images were made into a movie which shows the four moons in orbit several revolutions around the massive Jupiter.
Notice how the innermost moon Io orbits quickly. The farther moons more slowly. The planets of our solar system behave this way. All bodies in the universe orbit other bodies this same way. We are seeing from a unique perspective above the orbit plane. We are witnessing firsthand the effect of the law of gravitation. It is a thing of beauty. In addition, the three inner moons darken briefly as they pass into the shadow of Jupiter in each orbit.
“This is the king of our solar system, and its disciples going around it. It’s also representative of nature. This is how we look, that’s a mini solar system. And so, I think, to me it’s very significant because we’re finally able to see, with real video, real pictures, this motion. And we’ve only been able to imagine it up until today.”