No one told them to look for the Earth. It was Christmas Eve 1968 and the first manned mission to the moon had reached its destination. As Apollo 8 slipped into lunar orbit the crew prepared to read passages of Genesis for a TV broadcast to the world. But as the command module came around on its fourth lap, there it was visible through the window – a bright blue and white bauble suspended in the black above the relentless grey of the moon.

Before that moment 50 years ago, no one had seen an earthrise. The sight sent Bill Anders, the mission photographer, scrambling for his camera. He slapped a 70mm colour roll into the Hasselblad, set the focus to infinity, and started shooting though the telephoto lens.

What he captured became one of the most influential images in history. A driving force of the environmental movement, the picture, which became known as Earthrise, showed the world as a singular, fragile, oasis.

On previous laps Anders had snapped the far side of the moon for the geologists and the near side of it for Apollo’s landing site planners. “It didn’t take long for the moon to become boring. It was like dirty beach sand,” Anders told the Guardian. “Then we suddenly saw this object called Earth. It was the only colour in the universe.”

Apollo 8 launched from the Kennedy Space Centre in Florida on 21 December 1968. The enormous Saturn V rocket, more than 110 metres tall, had flown only twice before and never with a crew. But on that day the rocket performed.

An image of the planet taken by Apollo 17, on 7 December 1972, released by Nasa to celebrate Earth Day. Photograph: Nasa/Reuters

Tucked inside the command module, Anders, Frank Borman and James Lovell looped the planet twice before the third stage blasted them onwards to the moon. They arrived nearly three days later, completed 10 lunar orbits, and headed home for a splashdown in the north Pacific.

Earthrise did not have an immediate impact. Its philosophical significance sunk in over years, after Nasa put it on a stamp, and Time and Life magazine highlighted it as an era-defining image. “It gained this iconic status,” Anders said. “People realised that we lived on this fragile planet and that we needed to take care of it.”

The shot did more than boost the environmental movement. Even Anders, who calls himself “an arch cold war warrior”, felt it held a message for humanity. “This is the only home we have and yet we’re busy shooting at each other, threatening nuclear war, and wearing suicide vests,” he said. “It amazes me.”

The image changed his life more personally, too. “It really undercut my religious beliefs. The idea that things rotate around the pope and up there is a big supercomputer wondering whether Billy was a good boy yesterday? It doesn’t make any sense. I became a big buddy of [the scientist] Richard Dawkins.”

When the Apollo 8 mission splashed down on 27 December Anders thought it would not be long before tourists were gazing back on Earth from space hotels. “I thought that if I got a decent job and could make some money I could take my wife into orbit and view the beautiful planet we live on,” he said.

Fifty years later, commercial space hotels are still a distant dream. Anders says human space exploration went off track with the US space shuttle and the International Space Station. It was always a circular programme: the shuttle was built to fly to the station, and the station was built for the shuttle to fly to. But the shuttle did not live up to its billing as a cheap, reusable, space ferry.

“The shuttle ate Nasa whole but they never had the guts to cancel it,” he said. “It was like a cuckoo in the nest. It pushed out other good programmes to the point that when it finally died we had to hitch rides with the Russians to get back into space. That’s hardly something I would have considered in the process of beating the Soviets to the moon in 1968.” Anders says the space station, built for $150bn, has produced some interesting science but he thinks it was not worth the money.

Apollo 8 crew, from left, William Anders, James Lovell, and Frank Borman, visiting the Museum of Science and Industry, Chicago, April 2018. Photograph: JB Spector/AP

With the cold war over, Anders is wary of any human space exploration funded by the taxpayer. Under the latest plan the space station will be handed over to private industry; that frees up Nasa and other agencies to build a new, smaller, station orbiting the moon as well as a base on the surface.

“That is going to be massively expensive. Why do it? Who is going to pay for it?” said Anders. “I’m not against human space exploration but I am against giving our national debt another unbearable burden in order to pay for it. Humans right now are lost in space. There are some great unmanned programmes, some great commercial programmes, but the main programme? Right now, that’s screwed up.”

Anders likes to challenge what he sees as unchecked enthusiasm for human space missions. But to get him really vexed, mention sending people to Mars. Before he was assigned to the Apollo programme Anders worked on nuclear reactor shielding and radiation effects at the Air Force Weapons Lab in New Mexico. He understands how space radiation can be lethal to astronauts.

“It may be impossible for humans to go to Mars. You cannot carry the shielding you need to protect people. We’d need rockets 100 times bigger than the ones we have now. And even if you could, you have the zero-g to deal with.”

So he is not a fan of setting foot on the red planet? “The idea of going to Mars is, well, bullshit. The unmanned missions, they do a pretty good job of exploring Mars for science. What is it you’re going to get by putting men on the planet, except a horrific bill?”

Anders concedes perhaps he is now a grumpy old man. It is certainly hard to see him visiting schools to inspire the next generation of spacefarers. “Young people, they’re all excited, they want to be astronauts,” he said. “And I tell them no, don’t, it’s a big mistake. That’s the end of your scientific career.”

Anders has the Earthrise photograph hanging behind sun-protective glass in his living room. But it is not his favourite shot from the mission. That honour goes to a picture that captures the Earth in solitude, taken on the way out, when Borman had spun Apollo 8 around for a braking burn.

As much as Anders criticises human space exploration, the allure of orbit has never left him. “I feel cheated that I didn’t get to view Earth from Earth orbit. I’ve got some good friends who are space station astronauts and I envy them. They can kill time by looking out of the window and watching the Earth go by. I can do that on Google maps, but it’s not the same.”