Manhattan's east-west streets are thirty degrees off true east-west. That means the dates on which the sun sets directly parallel to the streets fall about three weeks either side of the summer solstice. Neil deGrasse Tyson, director of the Hayden Planetarium at the American Museum of Natural History, has coined the term Manhattanhenge for the two dates.
True Manhattanhenge, when half the sun's disk is above the horizon and parallel to the streets, is actually tonight. I took these photos last night on the bridge over 42nd St. in Tudor City, when the whole disk of the sun was sitting on top of the horizon. It draws quite a crowd. One person it didn't draw was a teenager talking into her cellphone "There's a bunch of people on the bridge taking pictures of the sunset or something. It's weird."
The best place to see the sunset is on the east side of Manhattan where you can see all the way across the island. The bridge may be crowded but it is a safe place to stand in the middle of the street.