CAPE CANAVERAL, Fla. — 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 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.

Celebrities, public figures, and other astronauts and scientists are happily obliging with videos. “What a day that was,” said actor Tom Hanks, who 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 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 after 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 in his video.

It’s the first big anniversary of the 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 of 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, also spent decades sidestepping the spotlight. But 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.

Aldrin, 84, 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.

“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 is asking people to post a video to YouTube using the hashtag (hash)Apollo45.

And the stories are pouring in.