July 11, 2008

A bridge at the end of a rainbow

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This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American

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Our Science Talk podcast host and man-about-town Steve Mirsky caught this lovely semi-circle rainbow with his pocket camera earlier this month. (Click on above image to play the Flash video.)

While you won’t find a pot of gold in this video, you will see a lovely view of something more useful to New Yorkers: the Triborough Bridge that links the Bronx, Manhattan and Queens. And today marks the 72nd anniversary of its completion by “master builder” Robert Moses on July 11, 1936.

Actually made of three bridges (a suspension bridge, lift bridge and truss bridge) the Triborough spans a total 2,780 feet, carrying eight lanes of traffic over three rivers: Hell Gate, Harlem River and Bronx Kill. Read more about the architectural and engineering feat here. To make the casings into which tons of concrete were poured, apparently an entire forest in Oregon was cut down (this from a reference to the epic book, The Power Broker, by Robert Caro).

It’s rare to see such a large half rainbow, and the reason for the size of a rainbow has to do with how our mind perceives it (this is influenced by the angle between the viewer and the sun.) There is no absolute position or size of any rainbow, hence why it appears to move as we move…and why that pot of gold is never found.

Want to know why it’s curved in the first place? Check out this “Ask the Experts” from our files.

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