Thursday, May 08, 2008

When is Manhattanhenge 2008?

Manhattanhenge occurs at sunset, 8:18PM EDT, on the 28 May at an azimuth of nearly 300°. By definition, sunset occurs when the Sun's trailing edge descends below our horizon , so one wants to arrive prior to 8:18PM to watch it entirety. 300° azimuth is 30° greater, or more northern, than cardinal point west, yet it corresponds to orientation of the cross streets of the Manhattan grid. Cross streets align along azimuths 120° on the east and 300° on the west, as depicted in the illustration below.

The Sun has an angular measurement around a half of a degree. The angular measurement of the street canyon from where I observed that sunset is slightly greater than my pinky held at arm's length, about a degree to a degree and one half ( 1° ~ 1.5°). In the schematic below the solar is disk is larger and brighter because of glare, the actual solar disk when observed through a solar filter is smaller, where nearly 3 solar disks could fit between the buildings.

At this time of the year the Sun lies on the ecliptic within the boundaries of the constellation Taurus. This is a section of the ecliptic where its angle with respect to the horizon is nearly perpendicular. In other words, the Sun sets on a steep angle so one can watch the sun set with more of a vertical drop rather than being carried across a shallow path.

If you miss the event or weather is afoul, one can still observe this on days leading up to or just past with the same effect. A list of the days , time of sunset and azimuth is provided below. Choose a cross street where you there is an unobstructed view to the western horizon. Any of the major cross streets work, like 23rd, 34th, 42nd, and 57th.

Don't forget to look behind you, your shadow is at its longest length, like the cone of night.

26 May, 8:16PM EDT --- 299° 29'
27 May, 8:17PM EDT --- 299° 43'
28 May, 8:18PM EDT --- 299° 56'
29 May, 8:19PM EDT --- 300° 09'
30 May, 8:19PM EDT --- 300° 21'

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