Between 1969 and 1972, 12 men walked on the moon. Four of them are still alive. No one has been back since, and it’s unclear when anyone might return.

The four moonwalkers were in their mid- and late thirties when they flew millions of miles to visit Earth’s celestial companion. Today, in their eighties, their hair is the color of the lunar surface. They remain in the public eye, giving talks and interviews, especially now, as the historic Apollo missions begin marking their 50th anniversaries. But someday, the moonwalkers will leave us, taking with them the living memory of a transcendent experience the rest of us can hardly fathom.

For the youngest generations, the idea of the moon landings, captured in crackly black-and-white footage, might seem as distant as the moon itself.