One day when I was in Junior High, we were playing Trivial Pursuit, and I was fascinated with one of the questions: "How many golf balls are there on the moon?" The back of the card said "three". I always remembered that, and would quote that little fact occasionally. I found out yesterday that it was wrong. There are two.

Two. Alan Shepard hit them February 6, 1971 right before they took off from the moon at the end of the Apollo 14 mission.

Some Sources Say Three

I found a number of sources online that say that there are three golf balls on the moon, even one on the nasa.gov site:

Alan Shepard is the only person to hit a golf ball on the Moon. During the Apollo 14 mission he fitted an 8 iron head to the handle of a lunar sample collection device and launched three golf balls. They are still there!

Source: http://www.nasa.gov/lb/facts/Space/space_facts_archives.html (as of 16-Aug-2007)

This is from NASA's "Space Facts Archive", a sort of list of trivia. In addition to inaccurately saying "three golf balls", this quote mentions an "8 iron". In the audio archive, Alan Shepad clearly says it's a "6 iron".

Funtrivia.com says: "There are 3 golf balls on the moon. Alan Shepard hit 2 and dropped 1." (http://www.funtrivia.com/askft/Question8379.html). Trivial Pursuit says three (in the 1980's anyway).

Real Answer: Two

Most sources I found say the right answer: there are two golf balls on the moon. However, since I had believed there were three for most of my life, I had to find a reliable source to convince me. The combination of these three things finally convinced me: a transcript of the interaction between Shepard and Houston, a video of him hitting the balls, and a 1991 interview with Shepard in which he says he took two balls to the moon.

Excerpt from transcript of communication (from http://www.hq.nasa.gov/alsj/a14/a14.clsout2.html):

135:08:17 Shepard: (Facing the TV) Houston, while you're looking that up, you might recognize what I have in my hand as the handle for the contingency sample return; it just so happens to have a genuine six iron on the bottom of it. In my left hand, I have a little white pellet that's familiar to millions of Americans. I'll drop it down. Unfortunately, the suit is so stiff, I can't do this with two hands, but I'm going to try a little sand-trap shot here. (Pause) [Jones - "He topped and buried it on the first swing. I assume that the six-iron was snuck on board."] [Mitchell - "In his suit pocket."] [The suits each had a utility pocket on the left thigh. During the EVA, Al and Ed wore a larger, strap-on pocket on the left thigh, 135:08:53 Mitchell: You got more dirt than ball that time.

Stuart Roosa, Alan Shepard, Edgar Mitchell 135:08:58 Shepard: Got more dirt than ball. Here we go again. [Al's second swing pushes the ball about 2 or 3 feet, mostly along the line toward the TV camera, rather than along the line of the swing.] 135:09:01 Haise: That looked like a slice to me, Al. 135:09:03 Shepard: Here we go. Straight as a die; one more. (Long Pause) [Al's third swing finally connects and sends the ball off-camera to the right, apparently on a fairly low trajectory. He drops a second ball, which rolls left and toward the TV camera. Al gets himself in position and connects again. The trajectory of this shot appears to be similar to the previous one.] 135:09:20 Shepard: Miles and miles and miles. 135:09:26 Haise: Very good, Al.

Excerpt from a transcript of an intervew with Alan Shepard in 1991 (From: http://www.achievement.org/autodoc/page/she0int-4 where you can also hear an audio version):

The deal I made with the boss was that if things were messed up on the surface, I wouldn't play with it, because we would be accused of being too frivolous. But, if things had gone well, which they did, then the last thing I was going to do, before climbing up the ladder to come home, was to whack these two golf balls. Which I did, and I folded up the collapsible golf club and brought it back with me. The balls are still up there.

Here's a link to a video of Alan Shepard hitting the golf balls: http://www.hq.nasa.gov/alsj/a14/a14v.1350811.ram

I think I can see why some people mistakenly thought there were three. Shepard swung four times. Everyone seems to agree his first swing completely missed and just kicked up some dust. He swung three more times, but only at two balls. The second swing moved the ball just a little ways. The third swing sent the first ball about 200 meters. Shepard then dropped the second ball, and his fourth swing (the first swing at the second ball) hit the ball and sent it about 400 meters.

As they were leaving, the astronauts took a picture that shows a javelin and one of the golf balls: (part of an image from http://www.hq.nasa.gov/alsj/a14/a14det9337.jpg):