Here's some food for thought: If future anthropologists dig up New York City someday and apply the same principles as we have for Stone Henge, it would look like the two days Manhattanites deem most important are May 28 and July 11, making Memorial Day and the Major League Baseball All-Star Game (essentially War and Baseball) cosmically critical to us.
For Manhattan (a place where evening matters more than morning), those are the two special days when the Sun sets in exact alignment with the Manhattan grid, fully illuminating every single cross-street for the last fifteen minutes of daylight.
Had Manhattan's grid been perfectly aligned with the geographic north-south line, then our special day would be the Spring equinox, and if we so designated, the Autumn equinox—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.
Read more from the Hayden Planetarium.