Depiction of Galileo demonstrating his astronomical telescope.2009 has been designated the International Year of Astronomy (IYA), in celebration of the 400th anniversary of Galileo first pointing the new invention of the telescope at the sky.
(Almost as famous as this act of opening our eyes to wonders we'd never witnessed, Galileo was tried by the Inquisition for pointing out that there were more things in heaven than were imagined by Church doctrine--but that's another story altogether…)
It's an intriguing fact that, beyond the Sun merely being a bright disk, the Moon a not-so-bright and slightly mottled disk, the stars pinpoints of light and the planets pinpoints of light that move, everything we have learned about the universe and the objects in it we have learned in the last four centuries, since the invention of the telescope and Galileo's putting it to it's most famous use: astronomy.
Galileo saw on the Moon craters, mountains, and valleys, and likened the "uneven, rough… depressions and bulges" to Earth's geographical features. Venus was revealed to undergo lunar-like phases, which provided controversial insight into the layout of the Solar System. Jupiter had four small "star-like" moons that moved around it--which defied Church doctrine holding that everything in the universe goes around the Earth. And Saturn possessed jug-handle-like protrusions, whatever those were!
It may be difficult to imagine what Galileo was feeling when he made these discoveries of things we take for granted. How exciting to peer through that celestial peephole and discover that the Moon is another world, and that there are worlds out there that had never been seen or imagined before. Sure, new discoveries about Mars keep rolling in, and we're finding a new extrasolar planet about every month--but the excitement about these discoveries is tempered by the fact that we already suspected things like these as possibilities. For Galileo, the magnified astronomical sky was practically a blank canvass.