The joke comes from the first time I went on a field trip to Meteor Crater east of Flagstaff, Arizona. Because I've done some work on the eroded impact craters of Titan, all I said was "Meh, I've seen bigger" because all the crater on Titan are bigger than the mile-wide Barringer crater.

A minor quibble with the summary above. On January 7, 1610, Galileo only recorded 3 "fixed stars" next to Jupiter. Two of the Galilean moons, Io and Europa, were too close together for Galileo to separate with his 20x power telescope. He continued to observe three moons at most, either because one or more moons were too close to Jupiter and were lost in the glare of the planet, Callisto was too far from Jupiter and was thus out of his telescope's field-of-view, or two of the moons were too close together, during subsequent nights, until January 13, when he was able to see all four for the first time.

Wikipedia is wrong on one point. True, his first observation of all four moon at once didn't come until January 13 and he didn't realize that there were four and not three until that time, but that doesn't mean that one moon's discovery (in Wikipedia's case, Ganymede) should be attributed to that date. By that point, he had observed all four on multiple occasions, just not all four at once. And to that point he hadn't even come to the conclusion that they were in orbit around Jupiter with their own separate orbits, moving a different speeds, until two days later, let alone ascribe identities to each of the stars he saw, connecting one star he saw with another from a different day, beyond the one to the east, the one to the west, and the one in the middle.