Forty years ago, on Dec. 7, 1972, three young men were on their way to the moon, racing away from the Earth at 25,000 miles per hour. Some ways out (about 28,000 miles), their ship passed a narrow tunnel of light, directly between the Earth and the sun. In that moment, they looked out the window and saw the Earth as almost no one had ever seen it: a giant, full, beautiful circle. The sands of the Sahara were in full sunlight. The snows of Antarctica shone bright white. The ocean resonated a deep blue hue.
At that point, one member of the Apollo 17 crew picked up a specially made Hasselblad camera and took several photos. No one knows who did this, because all three astronauts recalled taking the photo. Whomever did, it was a stunning, rare shot. You could see nearly all of Africa - the cradle of humanity - as well as the island of Madagascar, the Arabian peninsula and the clouds swirling over the ocean.
The photo would eventually become known as the "Blue Marble," and it would become one of the most enduring pictures of all time. In fact, that photo probably changed the way we viewed our place in the cosmos more than any other.
To be fair, the change was already underway. Four years earlier, astronauts brought back the famous "Earthrise" photo. Before that, in the face of acid rain and oil spills and DDT, we had begun to lose the sense that the planet was immense and inexhaustible. It had already started to seem smaller and more fragile than we had previously thought.
The Blue Marble was the perfect illustration of this feeling. Here you could see that our planet was an island of warmth, water and life in the black, cold ocean of space. The Blue Marble drove home just how beautiful the planet was, in the color and movement the photo captured. But there was something else: the edge. The void. The thin line between the blue and the black carried the most powerful message of all: Beyond that line, the Earth was finite.
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The photo became a global sensation, splashed across the pages of nearly every newspaper in the world. It inspired a children's TV show called "Big Blue Marble" and became the official Earth Day flag. It was printed on so many T-shirts, posters and bumper stickers -- "most any surface you can print on," as Al Reinert observed -- that it's hard to remember not having seen it at all.
The Apollo 17 astronauts flew on. They landed on the moon, scooped up some moon rocks and came home. But no one was very interested in their rocks. They were dusty and dead. Maybe that was why the public lost interest in going to the moon at all - there was nothing there for us, it seemed. No one has been back since.
Our thoughts had turned to our home.
Starting in 2002, NASA began trying to recreate the impact and excitement of Blue Marble by melding satellite images together so that it appeared in the form of planetary spheres from different angles. These images - known as the Blue Marble series - are beautiful, as well. Some are even breathtaking.
But when you see them, you know: They aren't real. There is something too perfect about them, too clear. They don't quite convince all the way. Forty years later, Blue Marble remains the only true photo of the whole planet; one of the few times a human eye has actually taken in the entire Earth.
Some astronauts, when they leave the Earth and watch it get smaller out their window, report a sudden overwhelming sense of how interconnected everything down there is. It's known as the "overview effect." And while most of us will never go into space, and never have that experience, in the Blue Marble, there has always been a bit of that feeling for us all to share.
Frank Bures is a writer in Minneapolis, Minn.
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