Since time immemorial humans have been intrigued by the little cluster of faint stars in the constellation Taurus called (in the Western tradition) the Pleiades. Six can be reliably seen with the unaided eye, although the ancients named seven Sisters. On a night of exceptional clarity, when my eyes were sharper, I have seen nine.
Galileo saw six. Then, in the winter of 1609-1610 he turned his newly-contrived telescope to the Pleiades and saw more than 40 additional stars, of which he mapped 36. He did the same for other nebulousities, the blur in Orion's sword, for example, but I like to take his observation of the Pleiades as a turning point in history, a first empirical confirmation of the radical opinion that the universe wasn't made explicitly for us. Giordano Bruno had a few years earlier gone to the stake for supposing as much without any observational evidence for doing to.
We no longer burn folks at the stake for such heresies, but the idea that humankind is a local and random cosmic phenomenon is still very much a minority opinion. I am happy enough to leave to the majority their self-defined centrality, as long as they are willing to allow me to follow Galileo into the stars. (Click to enlarge.)