In this July 20, 1969 file photo provided by NASA shows astronaut Edwin E. "Buzz" Aldrin Jr. posing for a photograph beside the U.S. flag deployed on the moon during the Apollo 11 mission. Aldrin and fellow astronaut Neil Armstrong were the first men to walk on the lunar surface. The trio was launched to the moon by a Saturn V launch vehicle at 9:32 a.m. EDT, July 16, 1969. They departed the moon July 21, 1969. (AP Photo/NASA, Neil Armstrong, File)

On July 20, 1969, Buzz Aldrin was "out of town" when the world united and rejoiced in a way never seen before or since.

He and Neil Armstrong were on the moon.

They missed the whole celebration 45 years ago this Sunday. So did Michael Collins, orbiting solo around the moon in the mother ship.

Now, on this Apollo 11 milestone—just five years shy of the golden anniversary—Aldrin is asking everyone to remember where they were when he and Armstrong became the first humans to step onto another heavenly body, and to share their memories online.

Too young? You can also share how the moonwalkers inspired you.

Celebrities, public figures, and other astronauts and scientists are happily obliging with videos.

"What a day that was," said actor Tom Hanks, sipping from an Apollo 11 commemorative cup. He starred in the 1995 film "Apollo 13," another gripping moon story.

"Going to space is a big deal. Walking on the moon is, literally, walking on the moon," said singer-songwriter Pharrell Williams, born four years afterward.

And from London Mayor Boris Johnson, who watched the event unfold on an a little black-and-white TV at an English farmhouse: "I knew immediately it was the most exciting thing that I'd ever seen. I was only 5 at the time. And it still is just about the most exciting thing I've ever seen."

In all, 12 men explored the moon in six landings through 1972. But that first moonwalk, by Armstrong and Aldrin, is what clinched America's place as space leader supreme following a string of crushing losses to the Soviet Union, which claimed title to first satellite, first spaceman, first spacewoman and first spacewalker.

"U.S. 1, Sputnik nothing," actor Louis Gossett Jr. said with a laugh in his video.

In this July 16, 1969 file photo provided by NASA, the Saturn V rocket that launched Neil Armstrong, Buzz Aldrin and Michael Collins on their Apollo 11 moon mission lifts off at Cape Kennedy, Fla. For the 45th anniversary of the Apollo 11 mission, Aldrin asked everyone to remember where they were when he and Armstrong became the first humans to step onto another heavenly body, and to share their memories online. (AP Photo/NASA, File)

It's the first big anniversary of man's first moon landing without Armstrong, whose "one small step ... one giant leap" immortalized the moment.

Armstrong, long known for his reticence, died in 2012 at age 82.

As Apollo 11's commander, Armstrong was first out the lunar module, Eagle, onto the dusty surface of Tranquility Base. Aldrin followed.

Collins, now 83, the command module pilot who stayed behind in lunar orbit as the gatekeeper, also spent decades sidestepping the spotlight. He's making an exception for the 45th anniversary—he plans to take part in a NASA ceremony at Kennedy Space Center on Monday to add Armstrong's name to the historic Operations and Checkout Building.

That leaves Aldrin, 84, as the perennial spokesman for Apollo 11. He will also be at Monday's ceremony.

"I consider myself a global statesman for space," Aldrin says in a YouTube video. "So I spend most of my time traveling the country and the world to remind people what NASA and our space program have accomplished, and what is still in our future at Mars. I feel we need to remind the world about the Apollo missions and that we can still do impossible things.

In this July 20, 1969 file photo provided by NASA, astronaut Edwin E. Aldrin Jr. walks on the surface of the moon, with seismogaphic equipment that he just set up. The flag like object on a pole is a solar wind experiment and in the background is the Lunar Landing Module. (AP Photo/NASA, Neil Armstrong, File)

"The whole world celebrated our moon landing. But we missed the whole thing because we were out of town. So now I invite you to share with me—and the world—your story or your family's story of where you were on July 20th, 1969. Or feel free to tell me how the Apollo missions inspired you."

Aldrin used to keep a little black book to list people's whereabouts on July 20, 1969. Everyone wanted to share that with him.

Now he's using social media and asking people to post a video to YouTube using the hashtag #Apollo45.

And the stories are pouring in.

This July 20, 1969 file photo provided by NASA shows a view of the Apollo Command Module with astronaut Michael Collins aboard as seen from the Lunar Module. Astronauts Neil Armstrong and Edwin Aldrin in the Lunar Module separated from Apollo 11 to prepare to go to the lunar surface. (AP Photo/NASA, File)

Peter Alyward, a self-professed space geek from Melbourne, Australia, recalls his parents waking him to see the Saturn V launch from what then was called Cape Kennedy, Florida, on July 16, 1969—45 years ago Wednesday—around the middle of the night Down Under.

It's the first major Apollo 11 anniversary— one divisible by five—that actually falls on the days of the week that the events occurred. Liftoff was, indeed, on a Wednesday, Eastern time; the moon landing was on a Sunday, Eastern time.

In this July 20, 1969 file photo provided by NASA, astronaut Neil A. Armstrong, Apollo 11 commander, smiles for a photo inside the Lunar Module while it rested on the lunar surface. Armstrong was first out the lunar module, Eagle, onto the dusty surface of Tranquility Base. (AP Photo/NASA, File)

"More than any other time in history, with the technology that became available then, all the people of the world truly did experience it and were able to share it. Not just as an American feat, but as a really global event," said Aylward, 56, a business developer for a software company.

Actor Tim Allen watched the moon landing from his boyhood Michigan home.

"To this day, it's the most exciting thing in my life, just to think what you saw and what you experienced ... " Allen said.

In this July 20, 1969 file photo made from a television monitor, Apollo 11 commander Neil Armstrong walks slowly away from the lunar module to explore the surface of the moon. Armstrong was first out the lunar module, Eagle, onto the dusty surface of Tranquility Base. (AP Photo, File)

Some of videos urge a return to the moon. President Barack Obama scrapped that idea in 2010 in favor of sending astronauts to an asteroid and then Mars.

"From one frontier to another, let's go back," Alaska's lieutenant governor, Mead Treadwell, said in his video.

This July 20, 1969 file photo provided by NASA shows Apollo 11 astronaut Neil Armstrong on the lunar surface. Apollo 11 astronauts trained on Earth to take individual photographs in succession in order to create a series of frames that could be assembled into panoramic images. This frame from Aldrin's panorama of the Apollo 11 landing site is the only good picture of mission commander Neil Armstrong on the lunar surface. Armstrong and fellow astronaut Edwin "Buzz" Aldrin spent nearly three hours walking on the moon, collecting samples, conducting experiments and taking photographs. In all, 12 Americans walked on the moon from 1969 to 1972. (AP Photo/NASA, Buzz Aldrin, File)

"Well done, Buzz Aldrin," added Johnson, London's mayor. "And about time we got back up there, huh?"

In this July 20, 1969 file photo provided by NASA, a footprint left by one of the astronauts of the Apollo 11 mission shows in the soft, powder surface of the moon. Commander Neil Armstrong and Edwin "Buzz" Aldrin became the first men to walk on the moon after blastoff from Cape Kennedy, Fla., on July 16, 1969. (AP Photo/NASA, File)

More information: #Apollo45: www.youtube.com/Apollo45

Buzz Aldrin: buzzaldrin.com/

NASA: www.nasa.gov/mission_pages/apollo/index.html

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