“Change,” Octavia Butler wrote, “is the one unavoidable, irresistible, ongoing reality of the universe.” And who am I to say we are done changing? Who am I to say that Butler was wrong when she wrote “The Destiny of Earthseed is to take root among the stars”? These days, I choose to believe that our persistence and our adaptability will allow us to keep changing with the universe for a very, very long time.

So far, at a paltry 250,000 years, it’s hard to give humanity’s temporal range more than one star. But while I initially found my brother’s words distressing, these days I find myself repeating them, and believing them. He was right. He always is. The species will survive this, and much more to come.

And so in hope, and in expectation, I give our temporal range four stars.

HALLEY’S COMET

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.

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.