Or the time...
You can see below what Galileo observed; in an animated gif.
Its was by plotting these changes in the positions of the galilean moons that Galileo was able to demonstrate that they were bodies that revolve around jupiter and therefore that all things did not revolve around the earth and hence this was another reason why it was not the center of the universe.
By National Aeronautics and Space Administration / Jet Propulsion Laboratory / Malin Space Science Systems - "Juno Approach Movie of Jupiter and the Galilean Moons" by NASAJuno on YouTube, Public Domain, Link
