When he first returned from space, William Shatner was overcome with emotion. The actor, then 90 years old, stood in the dusty grass of the West Texas desert, where the spacecraft had landed. It was October 2021. Nearby, Jeff Bezos, the billionaire who had invited Shatner to ride on a Blue Origin rocket, whooped and popped a bottle of champagne, but Shatner hardly seemed to notice. With tears falling down his cheeks, he described what he had witnessed, his tone hushed. “What you have given me is the most profound experience I can imagine,” Shatner told Bezos. “It’s extraordinary. Extraordinary. I hope I never recover from this.” The man who had played Captain Kirk was so moved by the journey that his post-touchdown remarks ran longer than the three minutes he’d actually spent in space.

Shatner appeared to be basking in a phenomenon that many professional astronauts have described: the overview effect. These travelers saw Earth as a gleaming planet suspended in inky darkness, an oasis of life in the silent void, and it filled them with awe. “No one could be briefed well enough to be completely prepared for the astonishing view that I got,” Alan Shepard, the first American in space, wrote in 1962, after he’d made the same trip that Shatner later took.

Beholding the silky clouds below, the continents and the seas, many astronauts have seen their home planet—and humankind’s relationship to it—in a profoundly new light. “It becomes so small and so fragile, and such a precious little spot in that universe that you can block out with your thumb,” Russell “Rusty” Schweickart, who spent 10 days orbiting Earth on the Apollo 9 mission, said in a 1974 speech.

Michael Collins, the Apollo 11 astronaut who flew around the moon, believed that if world leaders could experience the overview effect, intractable political differences might be resolved. “That all-important border would be invisible, that noisy argument suddenly silenced,” Collins wrote in his memoir, Carrying the Fire.

Gene Cernan, one of just a dozen people to have walked on the lunar surface, desperately wanted the rest of humanity to see what he had seen. “If only everyone could relate to the beauty and the purposefulness of it,” he said in 1985. “It wouldn’t bring a utopia to this planet for people to understand it all, but it might make a difference.”

“It becomes so small and so fragile, and such a precious little spot in that universe that you can block out with your thumb.”