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.
* * *
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.
* * *
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,