Manhattanhenge occurs when the setting sun aligns with Manhattan’s street...

Manhattanhenge occurs when the setting sun aligns with Manhattan’s street grid. Credit: Olivia Falcigno

Manhattanhenge, when the setting sun aligns with Manhattan’s street grid, will stop a city of 8 million in its tracks around 8:12 p.m. Wednesday.

That is when the full setting sun will be visible to anyone looking west along the borough’s parallel streets and out over the Hudson River (though no one should look directly into the sun), an effect similar to what the hunter-gatherers may have had in mind when they built Stonehenge in prehistoric England.

“It’s something everybody can go out and observe,” said Stony Brook University astrophysicist Frederick Walter. “If you’re in the city, it’s easy to do … You just go out and watch it.”

Two factors are at play, Walter said. The first is Manhattan’s street pattern, which is rectangular, with avenues running north-south and streets east-west — but only roughly. The actual orientation of the grid is rotated 30 degrees east from geographic north, so the Manhattanhenge effect does not occur when the sun sets exactly due west, but northwest.

The second factor is the apparent position of the sun when it rises and sets. Because the earth’s rotational axis is tilted, that point is constantly moving. For those of us in the Northern Hemisphere, it moves north until the first day of summer (officially, June 20 this year), then south until the first day of winter.

Full alignment — a sight that brings tourists and natives out in droves to some Manhattan intersections — happens twice a year, reoccurring this year on July 12. Half the sun will be visible Tuesday night and July 13.

Astrophysicist Neil deGrasse Tyson, who coined the name Manhattanhenge, described these moments poetically in an essay on the website of the American Museum of Natural History as “creating a radiant glow of light across Manhattan's brick and steel canyons, simultaneously illuminating both the north and south sides of every cross street of the borough's grid.”

Walter, whose professional interests lie in the birth and death of stars and space weather caused by solar activity, did not wax as poetic.

“I’ve seen pictures of Manhattanhenge,” he said. “It’s a bunch of people standing around in the middle of the intersection watching it and blocking traffic.”

Tyson, on the museum’s website, recommends viewers find a spot as far east as possible that still has views of New Jersey on main thoroughfares, including 14th, 23rd, 34th, 42nd and 57th streets. Tudor City Overpass in Manhattan and Hunter's Point South Park in Long Island City, Queens, are also possible viewing spots.

It was unclear if the weather would be conducive to viewing, however. After heavy weekend rain across the city and Long Island, National Weather Service forecasts so far for both areas predicted a 50% chance of showers and thunderstorms Wednesday night, with a sunny day giving way to clouds and daytime temperatures in the high 70s before dipping to 60 degrees at night.

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