The mission on the moon then over, astronaut Buzz Aldrin peaked out from the Apollo lunar module onto the powdery gray surface before him, the U.S. flag planted into it — just about the only color as far as the eye could see.
But as the ascent engines on the spacecraft came to life, carrying him and Neil Armstrong up, up, up, Aldrin caught a glimpse of something. Did the exhaust blow the $5.50 flag from its lunar foothold? Maybe. Probably.
Images taken by NASA's Lunar Reconnaissance Orbiter Camera more than 40 years later proved Aldrin right. Unlike the other Apollo sites, there is no longer an American flag still standing at the place where humankind first made contact with the lunar surface 50 years ago on July 20.
When people do return to our celestial partner, they likely won't find standing the most famous item that was left behind — a symbol of the nation's sacrifice and accomplishment. But they'll find other things: lunar landers and moon cars, camera gear and backpacks, a photo, maybe a few faded flags, some golf balls if they're lucky.
They'll find some more recent occupants, too, including an Israeli lander called Beresheet that crashed onto the surface in April.
But the Apollo missions were responsible for the largest chunk of the estimated 400,000 pounds of detritus left behind on the moon, a graveyard of spacecraft parts and symbolic items that was never supposed to be left undisturbed for so long. If current schedules hold, astronauts may stumble upon the remains as soon as 2024.
Here is what they may find:
96 BAGS OF HUMAN WASTE
When it came to defecating on or en route to the moon, astronauts had to rely on a pretty simple process: a bag taped to their bottoms. If all went well — that is, if it all ended up in the bag and not floating in the Apollo craft as sometimes happened — the waste would then be left on the moon as one of the many things discarded on the lunar surface to reduce the weight inside the spacecraft when it headed back to Earth.
The six Apollo missions that landed on the moon produced 96 bags of waste. According to the NASA History Office, white jettison bags, or trash bags, are definitely still on the moon, some containing astronaut poop.
Aldrin tweeted about it in April, saying, "Well, I sure feel bad for whoever finds my bag."
The astronaut, apart from being the second man who set foot on the moon, also holds another title: He was the first to urinate there.
According to space historian Teasel Muir-Harmony's book, Apollo to the Moon: A History in 50 Objects, Aldrin's urine collection device bag broke on a leap onto the lunar surface, leaking into his left boot.
"Everyone has their first on the moon," he said. The urine collection devices were also tossed overboard as the astronauts bid farewell to the moon.
WHAT'S LEFT OF THE AMERICAN FLAGS
Five decades of exposure to ultraviolet radiation and 500-degree temperature swings probably didn't create quite the nurturing environment needed to keep the five flags that remain on the moon in tip-top shape.
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Apart from the Apollo 11 flag, which is believed to have been lost, the others were planted during Apollo 12, 14, 15, 16 and 17. According to images captured by the Lunar Reconnaissance Orbiter during different times of day, shadows in the areas where the flags were planted indicate they're still standing.
Still, they're not likely to look like the well-known images of crisp red, white and blue flags stark against the bottomless black of space.
"You know how [if] you leave a flag out over summer, how it starts to fade," Arizona State University scientist Mark Robinson, the principal investigator of LRO's camera, told Space.com in 2011. "Now, imagine the extreme UV environment on the moon, and the hot and cold cycling … they're probably in pretty rough shape."
A FALCON FEATHER
In the final minutes of the Apollo 15 moon walk, Commander David Scott performed a small science experiment for the live television viewers back on his home planet.
He dropped a 0.06-pound falcon feather and a nearly 3-pound aluminum hammer from the same height at the same time. In the vacuum of space, they both hit the lunar surface simultaneously, confirming astronomer Galileo Galilei's theory that mass, or the weight of an object, doesn't have any effect on gravitational pull. The objects should fall at the same rate.
Because of the atmosphere on Earth, it doesn't quite work that way — but it does on the moon.
"How about that," Scott said when they hit the ground. "Mr. Galileo was correct in his findings."
The feather and hammer, it seems, are still there.
AN ASTRONAUT FAMILY PHOTO
Charles Duke was only 36 when he stepped on the moon during the Apollo 16 mission, the youngest man to do so. He was married to Dorothy Meade Claiborne and had two sons, Charles Duke III, who was 7 at the time, and Thomas Duke, 5, but was spending long periods of time away from his family in Houston while training in Florida.
"So just to get the kids excited about what dad was going to do, I said, 'Would y'all like to go to the moon with me?' " Duke told Business Insider in 2015. "We can take a picture of the family and so the whole family can go to the moon."
A friend from NASA, Ludy Benjamin, took a photo of the Dukes in their backyard, and on the back the astronaut wrote: "This is the family of Astronaut Duke from Planet Earth. Landed on the moon, April 1972." The kids signed it, too.
Duke shrink-wrapped the photo and fulfilled the promise.
"So I left that on the moon and took a picture of the picture," he told NASA in his 1999 oral history, "and that's one of our neatest possessions now."
COSMIC GOLF BALLS
Armstrong had the first step. Aldrin had the first tinkle. Alan Shepard had the first swing.
The astronaut and avid golfer told NASA in his 1998 oral history that he was intrigued by the idea that a ball hit by the same club head could travel "six times as far" in the airless environment on the moon.
"I thought, 'What a neat place to whack a golf ball!' " he said.
But to persuade NASA to let him do it, Shepard modified the handle used to scoop lunar samples and affixed an adapted club head to it. He took two golf balls with him, all of which he paid for.
"The two golf balls and the club at no expense to the taxpayer," Shepard said. He promised his boss, Bob Gilruth, the director of NASA's Manned Spacecraft Center, that he would wait to take the golf swing at the end of the Apollo 14 mission and only proceed if everything else had gone well.
So on Feb. 6, 1971, Shepard teed up his golf balls. Because of the bulkiness of his suit, he could only grab the club with his right hand. He shot. The first ball fell into a crater nearby but the second attempt was more successful.
"Miles and miles and miles!" Shepard called out as it soared away. The two balls are still there.
For years later, Shepard refused to say what brand the balls were, lest some company would try to profit from the information.
"There has been absolutely no commercialism. One company tried to say it was their golf ball, and we cut them off very quickly," Shepard told NASA. The astronaut sued a ball manufacturer who claimed to have made the moon balls.
"I've never told anybody," he is quoted as saying in his biography, Light This Candle: The Life and Times of Alan Shepard. "I've never told my wife."
But, as the biography's author, Neal Thompson, revealed: The balls were in fact made by Spalding.