From 2001, Neil deGrasse Tyson over at the Hayden Planetarium:
What will future civilizations think of Manhattan Island when they dig it up and find a carefully laid out network of streets and avenues? Surely the grid would be presumed to have astronomical significance, just as we have found for the pre-historic circle of large vertical rocks known as Stonehenge, in the Salisbury Plain of England. For Stonehenge, the special day is the summer solstice, when the Sun rose in perfect alignment with several of the stones, signaling the change of season.
For Manhattan, a place where evening matters more than morning, that special day comes on May 30th this year, one of only two occasions when the Sun sets in exact alignment with the Manhattan grid, fully illuminating every single cross-street for the last fifteen minutes of daylight. The other day is July 13th.
Had Manhattan’s grid been perfectly aligned with the geographic north-south line, then our special days would be the Spring and Autumn equinoxes, the only two days on the calendar when the Sun rises due east and sets due west. But Manhattan is rotated 30 degrees east from geographic north, shifting the days of alignment elsewhere into the calendar.
[H/t Linta Varghese]