A hammer and a feather – Apollo 15’s Galileo experiment

Many people consider Apollo 15 to be the crowning glory of the Apollo programme in terms of science. It’s therefore quite fitting that the crew managed to find time to pay homage to one of the most famous scientists of all time.

Crewed by Dave Scott, Al Worden and Jim Irwin, Apollo 15 was the first of NASA’s so-called ‘J’ missions, landings that focused on ‘extensive scientific investigation’ with the help of a Lunar Roving Vehicle.

On 30 July 1971, Scott and Irwin landed in Hadley Rille, a valley next to the Moon’s Appenine Mountains. They spent the next three days exploring the area using their rover, while Worden conducted experiments overhead in orbit.

(L-R) Dave Scott, Al Worden and Jim Irwin | Credit: NASA

In the late 1500s, Galileo Galilei theorised that, in a vacuum, objects would fall at the same rate of acceleration regardless of their mass. Where better to corroborate Galileo’s theory than on the Moon?

Towards the end of Irwin and Scott’s third and final EVA, Scott turned to address the TV camera, positioned on their rover, that was trained on the two astronauts.

He raised his gloved hands and said, “In my left hand, I have a feather. In my right hand, a hammer. One of the reasons we got here today was because of a gentleman named Galileo a long time ago who made a rather significant discovery about falling objects in gravity fields.”

“The feather happens to be, appropriately, a falcon feather,” Scott continued. It was a reference to the name of their lunar module, which in turn was named after the mascot of the United States Air Force Academy (Apollo 15 had an all-Air Force crew). “I’ll drop the two of them here and hopefully they’ll hit the ground at the same time.”

He let go of the hammer and the feather. Sure enough, they landed at the exact same moment.

“How about that?” Scott exclaimed. “Mr Galileo was correct in his findings!”

Scott watches as the hammer and feather fall to the surface of the Moon | Credit: NASA

The plan had been for Scott to bring the feather back with him, but in his excitement and haste to get everything wrapped up at the end of the EVA, he forgot to pick it up.

Should anyone in the future go back and revisit the Apollo 15 landing site, the feather will not still be resting where it fell. Scott carried out the experiment right in front of the lunar module, so it would presumably have been blown away to who knows where when Scott and Irwin ignited the lunar module’s ascent engine to leave the Moon’s surface.

Jim Irwin would later write, “I’m wondering if hundreds of years from now somebody will find a falcon’s feather under a layer of dust on the surface of the Moon and speculate on what strange creature blew it there.”

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