Mother Jones illustration; Getty; NASA/JPL-Caltech

On September 5, 1977, a 1,800-pound, ladle-shaped spacecraft named Voyager 1 took off from NASA’s Kennedy Space Center in Cape Canaveral, Florida, bound for the edge of our solar system. After about two months, it passed Mars’ orbit. Within two years, it made it to Jupiter, and almost two years after that, Saturn. On Valentine’s Day, 1990—34 years ago today—it looked back and snapped an image of Earth, the so-called “Pale Blue Dot,” which remains one of science’s most iconic photos, and, in my view, one of the greatest photos ever taken in the history of the world.

The first time I can remember seeing “Pale Blue Dot” was in high school. I’d won a print of the photo, appropriately, in a science fair competition. In the image, the Earth is about a pixel wide, a minuscule........

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