I'll be in NYC on Sunday and will try to get a few photos for anyone that is interested.

Obligatory appendix to this article:

How Far from True North are the Avenues of Manhattan? http://www.charlespetzold.com/etc/AvenuesOfManhattan/index.h...

When is Chicagohenge?

OK, I figured it out for myself: September 24 at 6:44PM. It also happened on March 18th at 7PM. I used "The Photographer's Ephemeris" (and some eyeballing) to determine this.