Fake Rainbows Lead to Scientific Discovery

By Gillian Mohney

Dec 7, 2011 3:38pm
ht simulated rainbow thg 111207 wblog Fake Rainbows Lead to Scientific Discovery

A simulated twinned rainbow. (Photo courtesy of Jacobs School of Engineering)

Yes, it’s a double a rainbow, but not one conjured up by Mother Nature. This is an artificial wonder, created by scientists at the University of California at San Diego, who used computer graphics to simulate rainbows to better understand the physics behind this natural phenomena.

While nature and computer graphics may seem an unlikely pairing, computer science professor Henrik Wann Jensen and Iman Sadeghi, who was working on his thesis, realized they could more accurately simulate rainbows in 3-D, where raindrops could be rendered as spherical, rather than the usual 2-D simulations, where raindrops are conveyed as circles.

Jensen, who has also created special effects on films such as “Avatar,” initially thought the project would merely be a way to  explore how accurately computers could  illustrate the irregularities found naturally in rainbows.

“It’s really the most basic phenomena, [but] when we saw these photographs, we said, ‘What’s going on?,’” Jensen told ABCNews.com. “We got the a-ha! experience.”

Through their detailed simulations, the scientists discovered the physics behind twinned rainbows in which a single arc branches out into two distinct rainbows. The team learned that the twinned effect is caused in part by the flattening of large raindrops as they fall through the atmosphere.

Dubbed “Burgeroids” (as in a compressed burger patty), the slightly compressed raindrops refract light slightly differently from smaller raindrops, which are spherical. When there are both small and large raindrops falling, the rainbow begins to fork, creating two different arcs.

“This goes beyond computer graphics,” Jensen said on the Jacobs School of Engineering website. “We now have an almost complete picture of how rainbows form.”

Sadeghi, now a software engineer in the graphics division of Google, was delighted with the unexpected discovery.

“You usually don’t get the opportunity to study such beautiful phenomena, while working on your Ph.D. thesis,” said Sadeghi on the Jacobs School of Engineering website. “There is a lot more to rainbows than meets the eye.”

After working on the project for years, Sadeghi said it’s difficult to view rainbows the same way.

“I saw a water sprinkler and I saw it made a rainbow and I could tell the size of the raindrops by the rainbow,” Sadeghi told ABCNews.com, laughing. “My eyes are totally distorted regarding these things.”

 

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