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Manhattanhenge creates some of its own natural wonders

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The Englishman W. M. Flinders Petrie, a noted Egyptologist, devised a numbering system for all the stones at Stonehenge. Simon Banton has created maps of all the stones of the entire site as well as a website with photos of each stone taken from several angles, which you can find at StonesOfStonehenge.org.uk.

Stonehenge, however, does not sit isolated in the middle of the Salisbury Plain. Aerial views clearly show a path 98 feet wide, defined by two parallel banks running 1.3 miles from the River Avon to Stonehenge, and called simply the Avenue. 

Sitting on the Avenue, 79 feet from the entrance to Stonehenge, is an important stone block which has helped galvanize the public’s fascination with the possible astronomical function of the site. It is a sarsen block known as the “Heel Stone,” which stands 16 feet tall, and leans toward the center of the monument.

The greatest public excitement at Stonehenge is generated the morning of the summer solstice when the sun rises in the northeast directly above the Heel Stone.  This position coincides with a specific point in the numbering system of the outer sarsen circle. Therefore, sunrise at summer solstice can also be seen from Stonehgenge’s center looking between Trilithon 30 (the last numbered stone in the outer sarsen circle) and the adjacent Trilithon 1. 

These stones are connected to each other by Lintel 101. The sight, whether from within Stonehenge, or by standing outside the circle, is spectacular. Just a reminder, trilithons are two upright sarsens connected by an overhead lintel. Think a doorway, or the letter pi.

However, if the sun rises at summer solstice, it also sets. Sunset takes place in the northwest and can be viewed through two different trilithons aligned in a straight line. The sun can be seen through the outer circle sarsens 21 and 22 overlaid by lintel 122, and then through the larger central trilithons 57 and 58, overlaid by lintel 158. 

This is a good moment to point out that there has been ongoing restoration work at Stonehenge. All three of these stones had fallen in 1900, and the lintel had even broken. They were repaired and repositioned in the 1950s. 

Winter solstice sunrise is in the southeast and sets in the southwest with other unique sightings through trilithons.

Before everyone rushes off to view Stonehenge, there are a few caveats. Totally free access is no longer possible. To enter during the year, you need to go with a private tour at special hours. The site is completely open only for Summer Solstice. The public can enter on the night before solstice at 7, and remain until 8 that solstice morning.

I believe you can now guess that Manhattahenge probably has to do with either the rising or setting sun in Manhattan. And you would be correct!

I always think of the Hudson River as running north-south and therefore, New Jersey lies due west of New York City and Riverdale. Well, not exactly. Much of Manhattan was laid out on a grid, but the east-west grid does not lie exactly due east (090 degrees) and due west (270 degrees), but is off by 29 degrees. And Riverdale streets, while less twisted off true, lies at 276 degrees off due west.

While there are no trilithons in Manhattan or Riverdale, there are plenty of skyscrapers in Manhattan and tall apartment buildings in Riverdale. Modern cities with these high buildings have led to the creation of the term “street canyons,” sometimes called “urban canyons,” which affect wind, temperature and air quality at ground level.

If Manhattan cross-streets were lined up perfectly due west, the sun would appear to set on the horizon viewed westward at the fall equinox in September. However, because of its 29-degree angle north of west, the Stonehenge effect of viewing the sun nestling perfectly between Manhattan’s tall buildings occurred on two dates this year — May 29 and May 30 as the sun was moving north toward spring solstice, and again July 12 and July 13  as it moves south toward winter solstice.

Riverdale, because of its different angle, should see the “Riverhenge” effect on Sept. 11, heading first toward equinox and then winter solstice, and March 31 (heading to spring solstice) on West 237th Street if you look westward from Henry Hudson Parkway. 

Kudos to the aforementioned Simon Banton. Reid Tillery helped me with the interplay between urban landscapes and astronomical events. 

Dr. Rao of the  Museum of Natural History was also very helpful and threw out the following question: “Why are people so interested in Manhattanhenge and so uninterested in so many more spectacular celestial events?” 

Thoughts appreciated!

Have a thought or comment for Sura Jeselsohn? Email her at greenscenesura@gmail.com.

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