Manhattanhenge: when the sun aligns spectacularly with the NYC street grid.
For 2014 the dates for Manhattanhenge fall on May 29th and July 12th, when the setting Sun aligns precisely with the Manhattan street grid, creating a lovely glow of light across the backdrop of the city, simultaneously illuminating both the north and south sides of every cross street of the borough's grid.
For these two days, as the Sun sets on the grid, half the disk sits above and half below the horizon. The day after (May 30th) and the day before (July 11) also offer Manhattanhenge moments, but at sunset, you instead will find the entire ball of the Sun on the horizon.
Half Sun on the Grid Times
Thursday, May 29 8:16 P.M. EDT
Saturday, July 12 8:25 P.M. EDT
Full Sun on the Grid Times
Friday, May 30 8:18 P.M. EDT
Friday, July 11 8:24 P.M. EDT
If you're going to check it out, then arrive a half-hour earlier than the times given above.
For best effect, position yourself as far east in Manhattan as possible. But ensure that when you look west across the avenues you can still see New Jersey. Clear cross streets include 14th, 23rd, 34th. 42nd, 57th, and several streets adjacent to them.