There's something magical about Manhattanhenge, the twice-a-year phenomenon when the sun sets exactly along the cross streets of New York City's prodigious grid.

Manhattanhenge is happening tonight at 8:16 p.m., which means, if you're in the city, you should head outside a few minutes before then if you want to really relish it. And you should! People love Manhattanhenge the way we love the shared experiences of a fireworks display or a cracking-loud thunderstorm—the kinds of moments that can feel bigger than they actually are, and turn out to be just as fun to anticipate as they are to experience.

Naturally, lots of people celebrate Manhattanhenge the way we organize around just about any event these days: by publicly processing our shared experience as it's happening. Manhattanhenge is often called an urban photographer's dream, and a major part of the appeal is to capture the perfect shot of the city bathed in gold as the sun dips behind long stretches of pavement. And yet the reason we like it so much in the first place has its roots in something ancient. More on that in a minute. First, a little history.

Manhattanhenge has really only been part of our culture for about a decade. Astrophysicist Neil deGrasse Tyson coined the term in 2002 as a portmanteau meant to evoke Stonehenge, where the sun aligns on the solstice. (Manhattanhenge doesn't coincide with the solstice because the city's grid alignment is not exactly north-south, but instead skews about 30 degrees off to the side.) Here's how deGrasse Tyson explained it last year:

You read anthropological books where they're always looking at some ancient culture. If they didn't have writing, you have to infer what they valued. So I thought: An apocalyptic Earth, if there's nothing that survives but our street grid, what would they say of us? Surely, future anthropologists would argue that we arranged our grid to align with the sun on purpose on those days, and what could they learn about our culture?

What they'd learn, perhaps, is something of the inherent tension between human construction and the natural environment. We have a tendency to think of cities as entirely built—concrete jungles, islands of pavement and glass—when really they are complex integrations with the natural world and the larger universe. Elements of nature—sunlight, trees, air, grass—are inextricable from how we think about city space and design. (At least, they are now. Urban planning has come a long way since the days of Robert Moses, the notorious Manhattan planner who cut off the city from the water that surrounds it.)