May 29, 2014

What Is 'Manhattanhenge?'

This Thursday marks a biannual solar event called Manhattanhenge, where the rising or setting sun aligns with the east-west grid of Manhattan streets. Astrophysicist Neil deGrasse Tyson coined the term back in 2002, inspired by the famous Stonehenge site in the United Kingdom, where the sun sets in alignment with the stones every summer solstice.

Technically, “Manhattanhenge” occurs around the summer solstice, not on the solstice itself. That’s because of the orientation of Manhattan’s famous grid pattern — established by the the Commissioners’ Plan of 1811 — is not perfectly aligned with the geographic north-south line; it’s rotated 29 degrees east, shifting the dates of alignment. If that alignment had been perfect, Manhattanhenge would have occurred on the equinoxes every year: the first day of spring and autumn, respectively.

(Historical side note: The goal of the 1811 plan was “a free and abundant circulation of air” to stave off disease. The right angles were also favored because “straight-sided and right-angled houses are the most cheap to build.” The rigid Manhattan grid has been much-maligned over the last 200 years, but recently has come back into favor with city planners.)

This kind of alignment is not unique to Manhattan; any city with a uniform street grid will have dates where the sun aligns with those streets, including Chicago, Toronto and Montreal.

But Manhattan also boasts a clear view of the horizon, looking across the Hudson River toward New Jersey. Plus you’ve got all those tall buildings lining the streets, creating the perfect vertical frame to show the setting sun to best advantage.

Read more at Discovery News

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