Four centuries ago this month, the Italian astronomer Galileo Galilei learned of a remarkable “toy” invented by a Dutch spectacle-maker the year before. Called a spyglass, this hollow tube with glass lenses at either end could make distant objects appear closer. Galileo quickly set out to design and construct one of his own. At first he was interested in the military potential of the gadget, but he soon used it as a way to bring the heavens closer.
