Speaking from Philadelphia during a stop on his book tour, he explains why being called “the second man to walk on the moon” bothers him, how stories about him seeing a UFO on the way to the moon are groundless, and why he is convinced that the United States will land a man on Mars within two decades.

There’s an amazing moment in your book when you look back at Earth from the moon and realize that of all the billions of people on Earth—living and dead—you, Neil Armstrong, and Michael Collins are the only three not there. Explore that feeling for us, Buzz.

It was an intellectual feeling. It certainly didn't make me feel lonely, except to realize that we were as far away as people had ever been. Once we were on the surface of the moon we could look back and see the Earth, a little blue dot in the sky. We are a very small part of the solar system and the whole universe. The sky was black as could be, and the horizon was so well defined as it curved many miles away from us into space.

View Images Courtesy of National Geographic Books

On the way to the moon, a strange incident occurred that was kept secret by NASA for many years. What is your view today about the UFO you thought you might have seen?

I'm surprised you're saying we saw a UFO and then covered it up. Nothing was covered up. I looked out and saw a light moving in relation to the stars. We didn't want to discuss anything that would make people think, Oh, Houston, there's a light following us to the moon! That would shake up a lot of people back on Earth. But we wanted to make an observation, so we innocently asked, Ground control, how far away is the upper stage rocket? They came back and said it's about 6,000 miles away. From my rendezvous experience I knew that there were four objects out there, which were the panels that sprung outward away from the rocket to expose the lander. Then, when we were in quarantine after returning to Earth, the higher management came in to talk to us from behind a window. Neil said, Guys, you were probably wondering why we asked you how far away the third stage rocket is. They said, Yeah that was puzzling. Neil explained it was because we saw a light, which was obviously the panels going out.

We assumed it was public knowledge and during an interview with the BBC I went through the whole story. The UFO people back in the United States became very angry with me—for not telling them first! [Laughs.] We knew it wasn't a UFO. But that doesn't stop the story from spreading among people who are looking for anything that they can call a cover-up or a UFO.

The famous phrase you used to describe the moon was “magnificent desolation.” Can you talk about that?

View Images Aldrin, photographed here at National Geographic headquarters in Washington, D.C., believes that within two decades America will lead international crews to land on Mars. Photograph by Becky Hale, National Geographic Staff

As the commander of the flight, Neil was going to be the one who first stepped onto the moon and said something historic, which he did. Then I come down and look around and nothing was prepared. If I had been the first to go down, I would've consulted philosophers or historians to help me come up with the right thing to say. But I wasn't the first. So I just put together words that came to mind to represent the magnificence of the human achievement. Throughout history we've dreamed of the moon, and wondered if people would ever go there. The magnificence of our achievement for humanity was that we were there. But when I looked around I saw the most desolate sight imaginable. No oxygen, no life, just the lunar surface that hasn't changed for thousands of years—and the blackness of the sky. It was the most desolate thing I could ever think of. And that’s why I said those words: the magnificence of the achievement and the desolation of where we were.

You, controversially, celebrated Communion on the moon with wine and bread you had “smuggled” aboard the spaceship. Talk about that incident—and whether you would do it again today.

Nothing was smuggled aboard. [Laughs.] Every little souvenir, every flag or coin we carried was counted and documented and carefully stored in the spacecraft. So a couple of weeks before we blasted off I thought it would be a good idea if I told the guy in charge of the flight crew what I was going to do. He said, Just don't talk about it when you are on the moon. When the Apollo 8 crew read from Genesis on Christmas Eve some people complained that, as a government-funded institution, NASA should not be promoting religion. So it wasn't until years later that I felt okay about talking about it.

I was involved, like John Glenn and some of the other astronauts, with a particular church. So I felt it was appropriate for me to demonstrate my Christian background. Today, my philosophy is more like what Albert Einstein called a cosmic sense of a greater power involved in the creation of the universe. It’s very nonspecific.

View Images After returning to earth, Aldrin (right) and the other Apollo 11 astronauts were quarantined in case they had brought unknown pathogens back to Earth. Here, they talk to President Richard Nixon shortly after splash down in the Pacific. Photograph by MPI, Getty Images

One of the surprises in your book is that, after the triumph of the moon landing, things fell apart for you. Your mother had killed herself and you battled alcohol abuse. Can you talk about that period of your life?

The title of my first autobiography was not Journey to the Moon. It was called Return to Earth, which was more descriptive of my situation coming back. After I left NASA, I hoped to be assigned to the Air Force Academy as commandant of cadets. I had been stationed there for a couple of years and I was an aide to the dean of faculty. But that assignment went to a classmate of mine from West Point, whose father was a four-star general in the Air Force.

Instead, I was assigned to command a test pilot school, which was rather ironic because I was somewhat unique on the crew, having never trained as a test pilot, as was required for all earlier astronauts. I was interested in space, not airplanes. So, after a year, I decided to retire from the Air Force. I'd already left NASA and wasn't anxious to join some corporation. So I was not sure what the rest of my life would be like.

When I returned from the moon I became a celebrity, a hero, with ticker tape parades and speeches. But that's not really what I looked for or desired. My mother had been unsettled by my celebrity status after my first space flight with Gemini 12 a few years earlier. And my older sister and I both came to the conclusion that perhaps that, along with other things, caused her to take her life. Her father, my grandfather, had also committed suicide, and my uncle had daughters who had committed suicide.

I began to think it was a genetic, inherited tendency. That brought me to consuming alcohol more and more and, of course, you can't straighten out something in your head unless you have a clear mind. You have to deal with obtaining sobriety first before dealing with other situations that are disturbing you. Today, I have 37 years of sobriety. If, occasionally, my mind gets the sense that the world around me is not doing what I'd like it to do, I may disappear for a day or even a week. That's something I've needed to deal with.

View Images "When I returned to earth I became a celebrity, a hero, with ticker tape parades and speeches," recalls Aldrin, shown here in Tokyo during a 1969 Goodwill Tour. "But that's not really what I looked for or desired." Photograph by Keystone/Hulton Archive/Getty Images

It was of course Neil Armstrong who made that “giant leap for mankind” by being the first man to walk on the moon. Does it upset you to be known as the second man on the moon?

At the time, not in the least. As the senior crew member, it was appropriate for him to be the first. But after years and years of being asked to speak to a group of people and then be introduced as the second man on the moon, it does get a little frustrating. Is it really necessary to point out to the crowd that somebody else was first when we all went through the same training, we all landed at the same time and all contributed? But for the rest of my life I'll always be identified as the second man to walk on the moon. [Laughs.]

Your favorite t-shirt says, “Get Your Ass to Mars.” Talk about your vision of a permanent settlement on the red planet. Isn’t that one dream too high?

No dream is too high. But, of course, going to Mars is much more difficult than going to the moon. It won't happen while I'm alive, unless I can live to 110. [Laughs.] But my son will hopefully be around to see it. He's working very diligently with the Buzz Aldrin Space Institute, which we formed in conjunction with the Florida Institute of Technology.

We are developing my plan, which is called Cycling Pathways to Mars. First, we will have a low-Earth orbit cycler. The second cycler will be a base at the moon that America designs but other countries help build and land. Crews will stay there for six months or a year, then come back to Earth to start to train as the first crew to land on Mars. I believe that within two decades America will lead international crews to land on Mars.

View Images Buzz Aldrin walks on the moon—and leaves his footprints. He famously described the lunar landscape as "magnificent desolation." Photograph by Neil Armstrong, NASA

What are the key lessons you would like to pass on to the next generation?

I've not had a flawless life. I've had to deal with many changes and challenges. I flew combat missions during the Korean War, lived through the threat of nuclear annihilation, and faced various challenges in the space program and my own life. Along the way, I discovered that I could contribute by using my innovation to think outside the box, in order to better serve my country. I took an oath to do that when I was 17 years old, and I've continued to be motivated by it, not by financial gain. I'm not driven by what comes back to me. It's the satisfaction of knowing that I'm helping to chart a course for others to bring nations together.

That's a very important part of it. I've been spending a lot of time looking for ways to increase our peaceful associations with China, the way we did with the Soviet Union, with a joint mission in space. We can do that with the Chinese and with other nations in an equal, productive way that is even better than the Apollo program.

What more significant a life could a person ask for? It’s a very busy life, but it's a tremendous opportunity for me to be of service to other people.

This interview was edited for length and clarity.