This occurs twice a year, on dates evenly spaced around the summer solstice. (sunset)
The first Manhattanhenge occurs around May 28, while the second occurs around July 12.
According to the Commissioners' Plan of 1811, the main traffic grid for Manhattan
is rotated 29° away from true east-west. Thus, when the azimuthfor sunset is 299°
(i.e., 29° North of West), sunset aligns with the streets on that grid.
A more impressive visual spectacle (and the one commonly advertised as Manhattanhenge)
occurs a couple of days after the first such date of the year, and a couple of days before
the second date, when a pedestrian looking down the centerline of the street towards
New Jersey can see the full solar disk slightly above the horizon and in between
the profiles of the buildings.[2]
The precise dates of Manhattanhenge depend on the date of the summer solstice,
which varies from year to year but remains close to June 21. In 2014, the "full sun"
Manhattanhenge occurred on May 30 at 8:18 p.m., and on July 11 at 8:24 p.m.[1]
The dates in which sunrise aligns with the streets on the Manhattan grid are
approximately December 5 and January 8 – spaced evenly around the winter solstice.
wiki
en.wikipedia.org/wiki/Manhattanhenge
上文讲了 夏至 和 曼哈吞悬日的关系, 冬至 向东看升日,夏至 向西看落日。