Get Ready for 'Manhattanhenge' on July 13

My favorite three-episode arc on CSI: New York follows Mac and his colleagues on a thrilling race against the clock to find and catch the so-called "Compass Killer," who has been randomly committing murders to the north, south, east and west of Manhattan island. Identified finally as Hollis Eckhart, a delusional schizophrenic who lost his wife, they still have no idea of where he will strike next.

But then, in an episode entitled "Manhattanhenge," Hawkes discovers Eckhart is using solar charts and astronomical instruments to guide him in his killings. It just so happens that December 5th, Eckhart’s birthday and the day of his wife's murder, is also the day where a biannual solar event called Manhattanhenge occurs, where the rising or setting sun aligns with the east-west grid of Manhattan streets.

Manhattanhenge is a very real phenomenon, and it's happening again this coming Wednesday, July 13. 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.

Tyson is the director of the American Museum of Natural History's Hayden Planetarium in New York City, and the museum will be marking the occasion with a special event Tuesday evening, July 12, featuring astrophysicist Jackie Faherty. Among other things, Faherty can tell you the best city locations by which to witness the phenomenon on July 13.

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: Chicago (September 25), Toronto (October 25 and February 16), and Montreal (July 12), for example.

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.

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