Why we only recently discovered space is dark not bright

A blue Earth ascends over the barren surface of the moon, against the black void of space. This famous photograph, Earthrise, was taken on Christmas Eve of 1968, by Apollo 8 astronaut Bill Anders.

After almost six decades, we take this image for granted. But imagine a different Earthrise, in which space isn’t black but bright blue, like the clear day sky. As strange as it may strike you, this is how most Europeans imagined it for centuries.

We know our understanding of the universe has undergone other major transformations, with far-reaching effects. For example, the shifts from an Earth-centred to a sun-centred universe and from a finite to an infinite universe weren’t only scientific discoveries. They made people genuinely rethink their place in the cosmos. The shift from a bright to a dark universe is of comparable significance, but it has been almost lost to history.

In recent years, through my research in literary history and the history of science, I have tried to piece together when this shift happened. When, so to speak, did space turn dark? And I’ve found myself asking: what happened to us in the process?

Consider the testimony of Domingo Gonsales, the protagonist of the first English science-fiction novel, Francis Godwin’s 1638 Man in the Moone. Travelling to the moon aboard a swan-powered spacecraft, Gonsales reports seeing very few stars – and these few, “by reason it was always day, I saw at all times alike, not shining bright, as upon the earth we… see them in the night time, but of a whitish colour, like that of the moon in the day time with us”. Why does he see fewer stars than we do from Earth? And why are they pale, like the moon seen in the daytime sky? Because his space simply is the daytime sky. The sun has dimmed the light of the brightest stars and drowned out completely that of fainter ones.

From our perspective, Gonsales’s universe is upside down. In his version, it is in daytime that we see it as it really is, whereas at night it is obscured by Earth’s dark shadow. But if we ascended into space at midnight, we would eventually break out of the shadow, into the eternal day beyond.

Gonsales doesn’t mention the shadow, but we catch a glimpse of it in another early space travel story, John Milton’s Paradise Lost. Approaching Earth, Milton’s Satan sees “the circling canopy / Of night’s extended shade”. In imagining a premodern Earthrise, then, we should add this shadow into the picture – a dark cone extending from the gibbous planet into the blue heavens and disappearing below the lunar horizon.

Other authors explain why space isn’t just bright, but bright blue. The most common explanation is that the “firmament” – the variously imagined vault of the cosmos – was blue in colour. This is the view, notes Milton’s contemporary, the atomist philosopher Walter Charleton, held “not only by vulgar, but many transcendently learned heads”. In looking at the day sky, they thought they were simply looking at the end of the universe.

The path towards Earthrise

This universe also appears in visual art. Here, again, comparison with Apollo 8 is instructive. Some hours after capturing Earthrise, the crew delivered a radio broadcast to Earth from lunar orbit. Commander Frank Borman wished Earthlings a merry Christmas and read from the biblical account of creation. For the first time, humans attained a comparable, godlike perspective on their blue planet, sparkling in the black abyss. But when premodern artists illustrated these same biblical verses, they often drew the inverse: dark Earths, suspended in azure heavens. To complete the alternative Earthrise, imagine one of these darker Earths, rather than the familiar “blue marble”, ascending over the lunar surface.

And it wasn’t just poets and painters. Philosophers and scientists also imagined such universes. Aristotle describes “the shadow of the earth (which we call night)”. Two millennia later, so does Copernicus, writing that “while the rest of the universe is bright and full of daylight, night is clearly nothing but the Earth’s shadow, which extends in the shape of a cone and ends in a point”.

There was nothing irrational about such views. Early European thinkers simply had no compelling evidence to the contrary, especially regarding the nature of outer space and of Earth’s light-refracting atmosphere. Without such evidence, why suspect that night is the rule and day the exception? What reason had a premodern Christian to break with centuries of tradition and no longer view the heavens – the abode of God, angels and blessed souls – as a realm of eternal light, but one of eternal darkness?

Which isn’t to say bright space was universal, even in premodernity. Thinkers of the Islamicate world, for example, accepted dark space from the 9th century onwards, though the reach of their views in the West seems to have been limited. By all accounts, dark space had to be rediscovered by European thinkers in the 17th century.

For one thing, the period saw major advances in the scientific understanding of the atmosphere. Indeed, “atmosphere” is a 17th-century word, and one of the first to use it in English was Walter Charleton, whose universe can be described as the missing link in the story: neither bright nor dark, but changing from one to the other as the observer turns towards and away from the sun. This is because Charleton’s universe is still bounded by a firmament – although a black one, “and not azure, as most suppose” – and is also filled with swarms of tiny particles or “atoms”, driving him to speculate about their visual effects. But for Otto von Guericke, who accepted an unbound, infinite universe, and made groundbreaking experiments studying the vacuum, space is, precisely, space. If we found ourselves in such “pure”, “empty” space, with “no body lighted by the sun either underneath or before” us, we would “see nothing other than shadow”.

From this point on, dark space is increasingly accepted by European scientists and scientifically literate thinkers. But that isn’t where the story ends, because bright space still survives for centuries in the popular imagination.

Fast-forwarding to 1858, here is the astronomer James Gall, imagining ascending into space in a work aimed at the Victorian general reader: “We look around, and oh, how strange! the heavens are black”. Gall knows space is black, but he doesn’t expect his audience to know it. And this audience isn’t necessarily uneducated in other departments. It isn’t an ignoramus or a child who, as late as 1880, still believes the universe is an “enormous sphere of blue” – it is a distinguished literary historian, David Masson. Isolated instances continue into the 1920s, the very doorstep of the Space Age.

We are dealing, then, not only with a lost, but also remarkably recent shift in our cosmological imagination. Because some of the most striking evidence appears in literary works, especially space travel narratives, it was first noticed by literary scholars: C. S. Lewis and, more recently, John Leonard. But it is yet to receive sustained study, and its cultural impact remains almost entirely uncharted.

This impact has been profound, although it often hides in plain sight. For example, it is widely recognised that images like Earthrise transformed our planetary and environmental consciousness. Earth became “whole” and “blue”, but also “fragile”: emblematic of the imperatives of political unity and ecological sustainability, as well as the threat of nuclear warfare and anthropogenic climate change. What isn’t recognised, however, is that this transformation wasn’t due solely to a new view of the planet, but also of what surrounded it.

Whole Earths had been imagined, depicted and reflected on since antiquity. But most floated in bright universes, eliciting very different reactions. The impact of Earthrise was therefore even greater than commonly understood. Once such images entered mass circulation, they wiped away even the last remaining vestiges of the old, bright cosmos, searing its exact inversion into the popular imagination: Earth as a luminous oasis in a dark cosmic desert. Earth was never “blue” or “fragile”, as such. It appeared so against the lethal darkness around it, which now became not only a scientific but also a cultural and psychological reality.

Mysteries of the universe: Cheshire, England

Spend a weekend with some of the brightest minds in science, as you explore the mysteries of the universe in an exciting programme that includes an excursion to see the iconic Lovell Telescope.