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Manhattanhenge

Manhattanhenge

by

Neil deGrasse Tyson, © 2001-2010

Sunset

looking down 34th Street. One of two days when the sunset is exactly aligned

with the grid of streets in Manhattan. Photo © Neil deGrasse

Tyson, 2001.

What

will future civilizations think of Manhattan Island when they dig it up and

find a carefully laid out network of streets and avenues? Surely the grid would

be presumed to have astronomical significance, just as we have found for the

pre-historic circle of large vertical rocks known as Stonehenge, in the

Salisbury Plain of England. For Stonehenge, the special day is the summer solstice,

when the Sun rises in perfect alignment with several of the stones, signaling

the change of season.

For

Manhattan, a place where evening matters more than morning, that special day

comes twice a year. For 2010 they fall on Sunday May 30th, and Monday July

12th, when the setting Sun aligns precisely with the Manhattan street grid,

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. A rare and beautiful sight. These two days happen

to correspond with Memorial Day and Baseball's All Star break. Future

anthropologists might conclude that, via the Sun, the people who called

themselves Americans worshiped War and Baseball.

For

these two days, as the Sun sets on the grid, half the disk sits above and half

below the horizon. My personal preference for photographs. But the day after

May 30th (Monday, May 31), and the day before July 12 (Sunday, July 11) also

offer Manhattanhenge moments, but at sunset, you instead will find the entire

ball of the Sun on the horizon.

Manhattanhenge times for 2010.

Arrive a half-hour earlier than the times given below.

Mock-up of the half sun on the grid during

Manhattanhenge.

Half Sun on the grid:

Sunday, May 30 — 8:17 P.M. EDT

Monday, July 12 — 8:24 P.M. EDT

Mock-up of the full sun on the grid during

Manhattanhenge.

Full Sun on the grid:

Monday, May 31 — 8:17 P.M. EDT

Sunday, July 11 — 8:24 P.M. EDT

For best effect, position yourself as far east in

Manhattan as possible. But ensure that when you look west across the avenues

you can still see New Jersey. Clear cross streets include 14th, 23rd, 34th.

42nd, 57th, and several streets adjacent to them. The Empire State building and

the Chrysler building render 34th street and 42nd streets especially striking

vistas.

Unnoticed

by many, the sunset point actually creeps day to day along the horizon:

northward until the first day of summer, then returning southward until the

first day of winter. In spite of what pop-culture tells you, the Sun rises due

east and sets due west only twice per year. On the equinoxes: the first day of

spring and of autumn. Every other day, the Sun rises and sets elsewhere on the

horizon. Had Manhattan's grid been perfectly aligned with the geographic

north-south line, then the days of Manhattanhenge would coincide with the

equinoxes. But Manhattan's street grid is rotated 30 degrees east from

geographic north, shifting the days of alignment elsewhere into the calendar.

Note

that any city crossed by a rectangular grid can identify days where the setting

Sun aligns with their streets. But a closer look at such cities around the

world shows them to be less than ideal for this purpose. Beyond the grid you

need a clear view to the horizon, as Manhattan has across the Hudson River to

New Jersey. And tall buildings that line the streets create a vertical channel

to frame the setting Sun, creating a striking photographic opportunity.

True,

some municipalities have streets named for the Sun, like Sunrise Highway on

Long Island and the Sunset Strip in Los Angeles. But these roads are not

perfectly straight. And the few times a year when the Sun aligns with one of

their stretches of road, all you get is stalled traffic solar glare temporarily

blinds drivers.

So

Manhattanhenge may just be a unique urban phenomenon in the world, if not the

universe.

Note

that a couple of years ago, an article in the New York Times identified this

annual event as the Manhattan Solstice. But of course, the word solstice

translates from the Latin solstitium, meaning stopped sun, in reference to the

winter and summer solstices where the Sun's daily arc across the sky reaches

its extreme southerly and northerly limits. Manhattanhenge comes about because

the Sun's arc has not yet reached these limits, and is on route to them, as we

catch a brief glimpse of the setting Sun along the canyons of our narrow

streets.

While

we are on the subject, when viewed from all latitudes north of the Tropic of

Cancer (23.5 degrees north latitude), the Sun always rises at an angle up and

to the right, and sets and an angle down and to the right. That's how you can

spot a faked sunrise in a movie: it moves up and to the left. Filmmakers are not

typically awake in the morning hours to film an actual sunrise, so they film a

sunset instead, and then time-reverse it, thinking nobody will notice.

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