A few hours later, near sunset, I placed myself in the wide-windowed cafe car to take in the expanse of the Nenana River Valley. Mount McKinley loomed high in the clouds to the left, the Alaska Range on all sides. Rockfall was indistinguishable from a stand of far-off spruce, mere middle shades in the chiaroscuro before us. The Nenana itself was blue, frozen, shot with cracks, a vast marble walkway on the valley floor.

If you ask friends to tell you why they are planning to visit Alaska in the winter, they’ll probably tell you they’re going for the Iditarod. To ski. To catch a glimpse of the northern lights. Of the mere tens of thousands of vacationers to the 49th state in the winter (compared with more than a million in the summer), these are the most common reasons for visiting.

But some people will shrug, give a far-off look, and say, “I’d just like to see it.” This is, perhaps, the truest reason of all. They come to reach out and touch, for a brief moment, the limits of human existence. To feel its chill and gaze into its twilight.

This was something I first began to understand as I sat in the cafe car of the Aurora Express at sunset, looking out on the snowscape. Across from me was Sam, a tourist from Taiwan who spoke almost no English. He strummed his ukulele. We began to sing “Let It Be” but could not remember all the words, so we sang the first verse and the chorus, over and over, louder each time. Other passengers joined in, filling the car. The sound was a comfort as we again slipped into darkness.

My family’s reason for visiting Alaska last winter was typical: We came to the dark in search of the northern lights, the aurora borealis, those magnetic storms of ionized oxygen and nitrogen atoms that play across the sky like warring gods. Our back story, though, is not exactly typical: My father, a retired programmer, earned his Ph.D. in astronomy in the early ’70s under Carl Sagan but never worked in the field. When I was a child, on clear nights when the magnetic activity was projected to be strong, my father would bundle us into the car and drive to Franklin D. Roosevelt State Park north of New York City on the off-chance that the aurora would be visible. These trips were our pilgrimages, our tests of faith in the idea that if we stood in a dark-enough spot at the right time, the heavens would open up and show what they held. Each time, my father kept us out in the cold until he could bear the complaints no longer. But we never saw the aurora. The heavens remained closed.