More than 50 years ago, the Apollo astronauts’ photographs of Earth seen from the moon had a jolting effect on a society distracted by division and conflict. Then, as now, they came in “an hour of change and challenge, in a decade of hope and fear, in an age of both knowledge and ignorance”, as President John F Kennedy had put it. But what he hadn’t predicted was that on the way to the moon, we would discover the Earth.

Here was our home planet, suddenly seen as a finite ball of rock, shrouded in an apple peel-thin layer of life-sustaining air. This view jarred with people’s everyday experience of living on the surface of an apparently infinite world of limitless resources. The creation of a special Earth Day soon followed, along with the founding of the campaigning environmental charity Friends of the Earth and the passing of a slew of environmental protection laws.

And for a brief moment, as the first moonwalkers toured the world, everyone who greeted them referred to their accomplishment as something that “we” did – “we the human race”, instead of an American achievement.

In the decades since then, no human has travelled far enough away to see Earth from such a humbling perspective. Human spaceflight focused instead on observations of Earth from a series of space stations around 250 miles high; only a thousandth of the distance that Apollo’s astronauts had seen it from. This is not far enough away to........

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