Why is this happening?
About 200 years ago, the architects who designed modern Manhattan decided to build a street network with avenues leading north and south and streets leading east and west. This choice set the stage for Manhattanhenge.
The sun moves slightly along the horizon throughout the year while the Earth tilts along its axis. That means there are times of year when the setting sun aligns with the streets running east and west in Manhattan.
If Manhattan were designed to face exactly east and west on a compass, Manhattanhenge would occur on the spring equinox and autumn equinox. Instead, the city is 30 degrees from Cardinal East and West, so the dates are offset.
Where are the best places to watch?
The key is to find a spot with a clear view of New Jersey, where the streets are wide and the buildings are beautiful.