The best description i've seen of this is "an urban solar phenomenon, with the Sun setting in alignment with the city's skyscrapers and giving an effect fans say is reminiscent of Wiltshire's Stonehenge".
Mighty statement for such an event, Mega high rise blocks of NY city & the effect of the sunrays of Father Sun setting for the evening casting beams of sunlight through the sidewalks of NY city.
Manhattan's Plan of 1811 established its grid system, which is rotated 29 degrees from true east-west. If Manhattan's streets were perfectly laid out on an east-west grid, Manhattanhenge would occur facing both east and west on the vernal and autumnal equinoxes.
For more info check out the Wikipedia link below
Manhattan Solstice aka Manhattanhenge