The Franklin Institute, Philadelphia

Sometime in late June or July 1609, Italian astronomer and physicist Galileo Galilei constructed his first spyglass—a simple contraption of lenses at the ends of a tube. The previous year in The Hague, a Dutchman named Hans Lipperhey had filed for a patent on the device, but it was Galileo who would go on to make it famous.

By the summer of 1609, Galileo, then a professor of mathematics in Padua, Italy, had managed to make a working model. His simple telescope would set off a revolution in the human understanding of the cosmos. He first used it to observe the moon and see the shadows cast by its mountains and craters; he went on to catalogue sunspots; and he discovered the four largest moons of Jupiter—Io, Europa, Ganymede and Callisto—that are now known as the Galilean moons in his honor.

Taken together, these observations would allow Galileo to support the Copernican view of the universe and not the Earth-centric view espoused by the church and by most educated men of the time. Galileo's discoveries would help supplant Ptolemaic astronomy, the vastly complicated and erroneous theory of celestial mechanics that had held sway for 1,400 years. (It has the dubious distinction of being among the longest-lived theories in science.)

In the centuries since Galileo first built his telescope, there have been huge improvements in the science, optics and technology behind the instrument. Today's state-of-the-art, Earth-based telescopes are mammoth structures, with flexible mirrors 10 meters across—devices that would have been completely unimaginable to Galileo and his immediate successors. Some of our clearest views of space have come from the orbiting Hubble Space Telescope, a technological wonder that continues to provide ever-improving glimpses into the universe nearly 20 years after its deployment. On the 400th anniversary of Galileo's spyglass, we take a look at some historic telescopes through the ages:

Slide Show: 10 Telescopes That Changed Our View of the Universe