By mid-1609, Galileo was working on his treatise about the science of motion, when upon hearing of the invention of the spyglass (the precursor to the telescope) he dropped everything to make his own version. By the end of August, Galileo had a 9X telescope. Around December 1, 1609, Galileo had in his possession a 20X telescope, allowing him to observe the moon’s rough mountainous surface, four (of the currently sixty-seven known) moons of Jupiter, and several new stars.
