It was the famed astronomer Galileo whose study of gravity spawned the legendary tale of the Leaning Tower of Pisa "feather drop." (The story is legendary in that historians believe the account may not be true.) However, as the story goes, Galileo held a feather and a stone in either hand and released them simultaneously. Because the feather's structure slowed its descent in parachute fashion, the stone reached Earth first. Had both been released above the Moon's surface, where no air exists, each would have struck lunar firmament simultaneously. It was not until Astronauts David Scott and Jim Irwin conducted Galileo's experiment on the Moon during their Apollo 15 mission that the experiment could be duplicated in the lunar environment.

Click here (2248 K .avi movie) to see and hear Apollo 15 Astronaut David Scott perform Galileo's experiment on the Moon. Galileo's hypothesis had been that all objects fall with the same acceleration in the absence of air resistance.