YouTube. Twitter. Facebook. Instagram. None of them existed in 1969. But 45 years later, they're all abuzz with memories of July 20, 1969, when the Apollo 11 space mission landed two men on the moon.

Buzz Aldrin was one of those two astronauts, and the second man to walk on the surface of the moon, after crewmate Neil Armstrong. Now, Aldrin is the face of the 45th Apollo 11 anniversary, working with NASA to celebrate the first lunar landing with a social media campaign that encourages people to submit their memories of the moon mission under the hashtag #Apollo45.

Armstrong died in 2012 at the age of 82, but NASA will rename a building in his honour at Florida’s Kennedy Space Center on Monday.

"Where were you when Apollo 11 landed on the moon?" the campaign asks. Aldrin and NASA have collected the video responses into a YouTube channel headlined by a number of famous individuals offering their own thoughts and memories on the historic event. From scientists like Stephen Hawking and Bill Nye, to celebrities like Stephen Colbert and Tom Hanks, the videos all touch on the significance of humanity's first steps on another world.

"This changed us," Nye says in his #Apollo45 YouTube video. "It made everyone believe that we could accomplish great things."

Among the YouTube tributes was one from Tim Allen, who voiced the Aldrin-inspired Toy Story character Buzz Lightyear, and who remembers watching the lunar landing as a boy. "To this day, it's the most exciting thing in my life, to think of what you saw and what you experienced, and how you moved everything forward," Allen says in a video addressed to Aldrin.

Star Trek and Star Wars: Episode VII director J. J. Abrams says in his video that he was only three years old at the time of the landing, but Apollo 11 remains an inspiration for the science fiction stories he produces now. "As wild and incredible as some of those stories may be, there is, in my mind, nothing more incredible than knowing that it actually has happened," he says.

American astrophysicist Neil deGrasse Tyson called it "extraordinary" that NASA managed to put humans on the moon just 10 years after the organization was founded in 1959. In his video, Tyson recalls watching the landing as a 10-year-old and thinking: "I now expect this to be a routine occurrence."

Noted astrophysicist Stephen Hawking says in his video that he didn't actually watch the moon landing because he was listening to a physics lecture. "There was no catch-up TV in those days, and we didn't have a television," he says. Hawking had to let his two-year-old son describe the landing to him.

Among the many Twitter tributes to the Apollo 11 mission was one from retired Canadian astronaut Chris Hadfield.

Neil Armstrong became the first man to walk on the moon on July 20, 1969. Aldrin followed in his historic footsteps minutes later. But to date, only 12 people have ever set foot on the lunar surface. The last manned mission to the moon happened nearly 42 years ago in December 1972.

The 84-year-old Aldrin is well past his astronaut days, but he's frequently voiced his support for pushing new frontiers with manned missions to Mars. "July 20th we landed on the moon. But my passion is future Mars missions," he said in a tweet posted last Tuesday.

One prospective Mars astronaut is a young boy named Michael, who posted a YouTube video to Aldrin earlier this week. The four-and-a-half-year-old wants to become an astronaut like Aldrin. "I want to go to Mars," he says in a video posted July 17. Michael appears in the video wearing an astronaut costume, and he addresses Aldrin directly. "You and (Apollo 11 astronaut) Mike Collins are my favourite astronauts."

The boy may be dreaming big, but he caught Aldrin's notice.

"It's kids like him I hope to inspire most about our future in space," Aldrin said in a tweet on Saturday.