Buzz Aldrin is asking everyone to remember where they were when he and Neil Armstrong became the first humans to step on to the moon, and to share their memories online.
On July 20, 1969, Aldrin and Armstrong were "out of town" when the world united and rejoiced in a way never seen before or since.
They missed the whole celebration 45 years ago this Sunday, and so did Michael Collins, who was orbiting solo around the moon in the mother ship.
Now, five years short of the golden anniversary, 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, who was born four years afterwards.
In all, 12 men explored the moon in six landings through until 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.
"US 1, Sputnik nothing," actor Louis Gossett Jr said with a laugh in his video.
It is the first big anniversary of man's first moon landing without Armstrong, whose "one small step ... one giant leap" immortalised the moment. He died in 2012 at the age of 82.
As Apollo 11's commander, Armstrong was first out the lunar module, Eagle, on to the dusty surface of Tranquility Base. Aldrin followed.
Collins, now 83, the command module pilot who stayed behind in lunar orbit as the gatekeeper, spent decades sidestepping the spotlight. He is making an exception for the 45th anniversary - he plans to take part in a Nasa ceremony at Kennedy Space Centre 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 travelling the country and the world to remind people what Nasa and our space programme 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 20, 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 is using social media and asking people to post a video to YouTube using the hashtag #Apollo45.