The photograph that Markisha McClenton posted on Instagram is a self-portrait, a close-up that is muted in dim light. She might be on her way to work. She might be coming home. Her workdays begin and end in the dark, and they are dark in between. She’s a lab technician in Jacksonville, Fla. Her specialty is blood. She has worked these dark hours since her son was 7. “Freedom,” she told me over the phone from her lab. That’s why she works these hours: The freedom to work at night and to raise her children during the days. To her, this is good fortune. She is smiling in this photo. But her eyes are midnight eyes, 3 a.m. eyes. Why take a photo at that hour? “People forget about us, the night shift,” she said. The #nightshift. That’s the hashtag she used. It’s how I found her.

I’ve been working at night myself for a long time now. Once it was out of choice, a preference for the quiet hours. More recently it was because I had no choice. Insomnia. One night, I was drinking my third cup of coffee — because when you can’t sleep, you might as well stop trying — and ignoring the deadline looming the next morning. Instead, I stared at the matrix on my phone, my own red eyes scanning a tiny sample of some 670,000 photographs under #nightshift. Most of them were people like me, awake when they didn’t want to be awake. And like me, they were looking at the screen in their hands, held up by the one in mine.

This is the ghost world of #graveyardshift (#nightshift’s sister hashtag), whose workers file into Instagram every evening. These pictures may be clever or maudlin, silly or harrowing or sad. “Desperate” is a word that comes to mind, but so does “resigned.” And even “resistance.” Sometimes it’s in the form of a gag, a ridiculous pose; sometimes it’s in the form of a gaze so steady that it seems to warm the fluorescent panels framing so many of these pictures. The hashtag itself is a form of solidarity.

There are the warehouse workers who snap themselves letting a wisp of marijuana smoke slip from between their lips, little Instagram rebellions. There are the soldiers and sailors pulling a night shift for no good reason other than orders, photographing themselves and their comrades on the verge of sleep or already under. Cops in noirish black and white, their pictures framed to show a bit of badge. And nurses. A lot of nurses. Close-up, arm’s length, forced smiles, dead eyes. Scroll through #nightshift, and you’ll see some saints among them and some whose hands you hope will be more alive in an emergency than their ashen faces.