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The Pale Blue Dot

The most famous photograph of Earth shows almost nothing: a dot smaller than a single pixel, taken by a dying camera four billion miles from home.

In plain English

On 14 February 1990, a space probe called Voyager 1 turned its camera around and photographed the planet it had left thirteen years earlier. It was six billion kilometres away by then, further from the Sun than any camera had ever been.

In the picture, Earth is a speck. Not a small circle, not a marble: a speck, 0.12 of a single pixel, caught by chance inside a stray beam of scattered sunlight. Everything that has ever happened to anyone happened on that speck.

Thirty-four minutes after taking it, Voyager's cameras were switched off to save power, and they have never been switched on again. The last thing the spacecraft ever looked at was home.

Five things to file under "wait, what?"

  • Earth is less than a pixel. From that distance our planet subtends 0.12 of a pixel in Voyager's narrow-angle camera. The dot you see in the published image is bigger than the planet actually appeared, because light bleeding into neighbouring pixels enlarged it. The photograph is famous for showing almost nothing.

  • The sunbeam is a fault, not a feature. The shaft of light Earth sits in is lens flare: sunlight scattering inside the camera because the shot was aimed so close to the Sun. An optical imperfection became the whole composition, a world suspended in a sunbeam by accident.

  • It was nearly never taken. Carl Sagan first proposed the picture in 1981 and pushed for the better part of a decade. There was no scientific case for it, engineers worried that pointing so near the Sun could damage the optics, and mission time cost money. It finally happened only because the cameras were about to be shut down anyway: there was nothing left to lose.

  • It was one frame of a family portrait. Voyager took 60 images that day, sweeping across the solar system to capture six planets in one mosaic: the only portrait of our solar system from the outside. Mercury was lost in the Sun's glare and Mars was too faint to catch. The pictures trickled home over weeks that spring, radioed back at a rate slower than a 1980s modem.

  • The photographer is still going. Voyager 1 is now some 25 billion kilometres out, four times further than when it took the picture, and is the most distant human-made object there is. It crossed into interstellar space in 2012 and still radios home daily, on a transmitter using about as much power as a fridge bulb.

The full story

Why there was no scientific reason to do it

By 1990, Voyager 1's work was done. It had flown past Jupiter in 1979 and Saturn in 1980, returned tens of thousands of images, and been flung on a path climbing away from the plane of the planets. From its position there was nothing left to photograph that science needed: the planets were pinpricks, the spacecraft was receding at seventeen kilometres a second, and every instrument watt mattered for the decades ahead.

Sagan wanted the picture anyway, and he was clear about why. Not data. Perspective. He had watched the Apollo Earthrise photograph change how people talked about the planet, and he believed a picture of Earth from the edge of the solar system would finish the thought: not a blue marble, but a mote.

The shot itself

The pictures were taken about 32 degrees above the plane of the solar system, looking back down at it. For Earth, the camera had to point perilously close to the Sun, which is why the frame is streaked with scattered light. The exposure caught our planet as a fraction of a pixel of pale blue, the colour coming from sunlight scattered by air and ocean.

Then the cameras were commanded off. Voyager's plutonium power source loses a few watts every year, and every subsystem that could be spared had to go. The camera software was later deleted from the onboard computers entirely. Even if you wanted to turn them back on, there is nothing left to turn on.

What Sagan said about it

Four years later, Sagan published the passage that made the photograph immortal, and it is worth reading slowly rather than quoting at length. The heart of it: "Look again at that dot. That's here. That's home. That's us." Everyone who has ever lived, he pointed out, every saint and tyrant, every civilisation, every war fought over a corner of the frame, happened on a fraction of a pixel suspended in a sunbeam.

It is often read as a humbling. It is really an argument: seen from six billion kilometres, the case for being kinder to one another and for looking after the dot writes itself.

Where the picture went next

For the photograph's thirtieth anniversary in 2020, NASA reprocessed the original data with modern techniques, brightening the sunbeam and leaving the Earth exactly as it was: still less than a pixel. Nothing has photographed Earth from further away since, and nothing currently flying ever will. Voyager 1's cameras are gone, and no other spacecraft is on a path anything like as distant.

The probe itself carries the Golden Record, a gold-plated disc of music, greetings and sounds of Earth, chosen by a committee Sagan chaired. It will outlast the planet's continents. The dot, meanwhile, is the only home anyone has ever had, which was rather the point.

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