I'm not really much on repeating things from other people's blogs, but I found this on bldgblog and it seemed cool enough to repeat:
"As it happens, then, Manhattan's mathematically rational street grid is actually rotated 29º off the north-south axis – and this angle has interesting astronomical side-effects... because of the off-center orientation of Manhattan's street grid, you can only see the setting sun "down the middle of any crosstown street" on two specific days of the year: May 28 and July 13. July 13 is, of course, next week – so watch out for it."
This reminds me of both Aztec and Khmer city building, in which cities actually functioned as giant calenders.
If I were in New York, I think I'd throw some kind of party.