Twice a year, the setting sun aligns perfectly with Manhattan’s city grid of streets, and the sun peers down the building canyons at sunset. The first set occurs May 29th and 30th, 2008. If you situate yourself to watch the sunset anywhere along Manhattan’s east-west corridors, you can observe this effect, starting a little before 8pm, lasting until the sun disappears from view.

If Manhattan’s grid had been built aligned on the geographic north-south line, then the days of Manhattanhenge would be the spring and fall equinoxes, but it occurs on other dates because Manhattan’s street grid is rotated 30 degrees east from geographic north. (The other days in the year this occurs in 2008 are July 11th and 12th, around 8:25pm.)

See Video
Hayden Planetarium Director Neil deGrasse Tyson (host of Nova’s ScienceNow) coined the term “Manhattanhenge”, and he has a video on NOVA Dispatches that illustrates this rare occurrence, in case you’re nowhere near the island tonight.