Atlantic poetically says: "Where nature meets the grid, we find an ancient way of meeting the cosmos." It's also a chance of a bit of us-vs-themisim, pedestrians vs motorists since photographing the alignment of sunset with the E-W grid of Manhattan's streets requires standing in the middle of 14th, 23rd or 57th St. — viewing points precisely because they are the main thoroughfares that cut all the way across the island — at the tail end of the evening commute.
I love Neil Degrasse Tyson's observation that post-apocalyptic New York anthropologists will have to conclude that the city was arranged this way for some kind of cryptic ceremony of sun worship.
In a similar but less-physcis, more-crazy vein, I overheard the following conversation:
Man with God complex: No pictures! No pictures! And by that, I mean I am God, Shannon.
Erica: No, it's Erica, but it's okay. You've got a lot of people to keep track of.
Other New Yorkers were less philosophical:
Girl to her friend: What if this is how I die?
Hipster 1: ... and the sun sets directly between the buildings.
Hipster 2: So what?
Woman crossing the street, to me: Who are we taking pictures of?
Me: It's called Manhattanhenge. It's when —
WCTSTM: Oh, yeah. That.
Tourist: Maybe it's Sarah Jessica Parker!