ONE OF THE ENDURING MYSTERIES of Halley’s comet is that nobody knows how to spell its name, as the comet is named for an astronomer who spelled his own surname variously as Hailey, Halley, and Hawley. We think language moves around a lot these days, with the emergence of emojis and the shifting meaning of words like literally, but at least we know how to spell our own names. I’m going to call it Halley’s comet, with apologies to the Hawleys and Haileys among us.

It’s the only periodic comet that can regularly be seen from Earth by the naked eye. Halley’s comet takes between seventy-four and seventy-nine years to complete its highly elliptical orbit around the sun, and so once in a good human lifetime, Halley brightens the night sky for several weeks. Or twice in a human lifetime, if you schedule things well. The American writer Mark Twain, for instance, was born as the comet blazed above the Missouri sky. Seventy-four years later, he wrote, “I came in with Halley’s Comet in 1835. It is coming again next year, and I expect to go out with it.” And he did, dying in 1910 as Halley reappeared. Twain had a hell of a gift for narrative structure, especially when it came to memoir.

Seventy-six years later, the comet returned in the late winter of 1986. I was eight. This apparition of the comet was, to quote Wikipedia, “the least favorable on record,” with the comet much farther from Earth than usual. The comet’s distance, combined with the tremendous growth of artificial light, meant that in many places Halley was invisible to the naked eye.

I was living in Orlando, Florida, a town that throws a lot of light up at the night sky, but on Halley’s brightest weekend, my dad and I drove up to the Ocala National Forest, where our family owned a little cabin. At the tail end of what I still consider to be one of the best days of my life, I saw the comet through my dad’s birding binoculars.

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Humanity may have known that Halley was a repeating comet thousands of years ago. There is a reference in the Talmud to “a star that appears once in seventy years and makes the captains of ships err.” But back then it was common for humans to forget over time what they had already learned. Maybe not only back then, come to think of it.

At any rate, Edmond* Halley noticed that the 1682 comet he observed seemed to have a similar orbit to comets that had been reported in 1607 and 1531. Fourteen years later, Halley was still thinking about the comet, writing to Isaac Newton, “I am more and more confirmed that we have seen that comett now three times since ye year 1531.” Halley then predicted the comet would return in 1758. It did, and it has been named for him ever since.

Because we so often center history on the exploits and discoveries of individuals, it’s easy to forget that broad systems and historical forces drive shifts in human understanding. While it is true, for example, that Halley correctly predicted the comet’s return, his colleague and contemporary Robert Hooke had already expressed “a very new opinion” that some comets might be recurring. Even putting aside the Talmud’s possible awareness of periodic comets, other sky gazers were beginning to have similar ideas around the same time. Seventeenth-century Europe—with not just Newton and Hooke, but also Boyle and Galileo and Gascoigne and Pascal—saw so many important scientific and mathematical breakthroughs not because the people born in that time and place happened to be unusually smart, but because the analytic system of the scientific revolution was emerging, and because institutions like the Royal Society allowed well-educated elites to learn from one another more efficiently, and also because Europe was suddenly and unprecedentedly rich. It’s no coincidence that the scientific revolution in Britain coincided with the rise of British participation in the Atlantic slave trade and the growing wealth being extracted from colonies and enslaved labor.

We must, then, try to remember Halley in context—not as a singular genius who emerged from a family of soap-boilers to discover a comet, but as a searching and broadly curious person who was also, like the rest of us, “a bubble on the tide of empire,” as Robert Penn Warren memorably put it.

That noted, Halley was brilliant. Here’s just one example of his use of lateral thinking, as discussed in John and Mary Gribbin’s book Out of the Shadow of a Giant: When asked to work out the acreage of land in every English county, Halley “took a large map of England, and cut out the largest complete circle he could from the map.” That circle equated to 69.33 miles in diameter. He then weighed both the circle and the complete map, concluding that since the map weighed four times more than the circle, the area of England was four times the area of the circle. His result was only 1 percent off from contemporary calculations.

Halley’s polymathic curiosity makes his list of accomplishments read like they’re out of a Jules Verne novel. He invented a kind of diving bell to go hunting for treasure in a sunken ship. He developed an early magnetic compass and made many important insights about Earth’s magnetic field. His writing on Earth’s hydrological cycle was tremendously influential. He translated the Arab astronomer al-Battānī’s tenth-century observations about eclipses, using al-Battānī’s work to establish that the moon’s orbit was speeding up. And he developed the first actuarial table, paving the way for the emergence of life insurance.

Halley also personally funded the publication of Newton’s three-volume Principia because England’s leading scientific institution, the Royal Society, “rashly spent all its publishing budget on a history of fish,” according to historian Julie Wakefield. Halley immediately understood the significance of the Principia, which is considered among the most important books in the history of science.* “Now we are truly admitted as table-guests of the Gods,” Halley said of the book. “No longer does error oppress doubtful mankind with its darkness.”

Of course, Halley’s ideas didn’t always hold up. Error still oppressed doubtful humankind (and still does). For example, partly based on Newton’s incorrect calculations of the moon’s density, Halley argued there was a second Earth inside of our Earth, with its own atmosphere and possibly its own inhabitants.

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By the time Halley’s comet showed up in 1986, the scientific revolution’s approach to knowledge-building had proven so successful that even third graders like me knew about the layers of the earth. That day in the Ocala National Forest, my dad and I made a bench by nailing two-by-fours to sections of tree trunk. It wasn’t particularly challenging carpentry, but in my memory, at least, it took us most of the day. Then we started a fire, cooked some hot dogs, and waited for it to get properly dark—or as dark as Central Florida got in 1986.

I don’t know how to explain to you how important that bench was to me, how much it mattered that my dad and I had made something together. But that night, we sat next to each other on our bench, which just barely fit the two of us, and we passed the binoculars back and forth, looking at Halley’s comet, a white smudge in the blue-black sky.

My parents sold the cabin almost twenty years ago, but not long before they did, I spent a weekend there with Sarah. We’d just started dating. I walked her down to the bench, which was still there. Its fat legs were termite-ridden, and the two-by-fours were warped, but it still held our weight.

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Halley’s comet is not a monolithic spherical miniplanet flying through space, as I imagined it to be. Instead, it is many rocks that have coalesced into a peanut-shaped mass—a “dirty snowball,” as the astronomer Fred Whipple put it. In total, Halley’s dirty snowball of a nucleus is nine miles long and five miles wide, but its tail of ionized gas and dust particles can extend more than sixty million miles through space. In 837 CE, when the comet was much closer to Earth than usual, its tail stretched across more than half of our sky. In 1910, as Mark Twain lay dying, Earth actually passed through the comet’s tail. People bought gas masks and anti-comet umbrellas to protect against the comet’s gases.

In fact, though, Halley poses no threat to us. It’s approximately the same size as the object that struck Earth sixty-six million years ago leading to the extinction of dinosaurs and many other species, but it’s not on a collision course with Earth. That noted, Halley’s comet will be more than five times closer to Earth in 2061 than it was in 1986. It’ll be brighter in the night sky than Jupiter, or any star. I’ll be eighty-three—if I’m lucky.

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