A young Galileo is perched atop the Leaning Tower of Pisa. He is in the middle of his famous experiment—the one in which he shows, by dropping cannonballs of different weights, that all objects ...

Galileo was the first to discover the moons of Jupiter. Michael Benson / Kinetikon Pictures / Corbis (Jupiter) / Scala / Art Resource, NY (Galileo) Inside a glass case was a plain-looking tube ...