The words "double rainbow" are now somewhat famous thanks to the YouTube clip about seeing, yes, a double rainbow.

Twinned rainbows are the subject of a new research paper from a team of scientists at UC San Diego and Disney Research.

Double rainbows are unusual - and are certainly cause for excitement in the clip - but they aren’t nearly as rare as twinned rainbows. While double rainbows follow the same arc, twin rainbows start at the same point but follow slightly different paths so they end up looking something like a rainbow-colored “V.”

Twinned rainbows are the subject of a new research paper from a team of scientists at UC San Diego, Disney Research and Universidad de Zaragoza in Spain. Disney Research started in 2008 as a collaboration between Disney and research labs like Carnegie Mellon University and the Swiss Federal Institute of Technology Zürich.

Wojciech Jarosz, a Disney researcher who studied at UCSD, said they made their discovery somewhat by accident. It started when they were simply trying to find out more about how rainbows work.

“Everybody finds rainbows really fascinating and it was an interesting technical challenge to figure out how we could render these things mainly for the purpose of games or movies, and at the time we thought that this was pretty well understood by science but it turned out there were a number of rainbow phenomena that couldn’t be well explained,” he said.

The team studied simulations of virtual rainbows made by different shapes of water drops and how those drops reflected light. They found twin rainbows are caused by different sizes of water drops falling from the sky at the same time.

The next step, Jarosz said, is to recreate the scenario in the real world to see if their theory is right.

“One thing to do in the future would be to create a shower synthetically in the real world which is made of different types of water drops and see if we can actually produce a twinned rainbow physically,” he said.

Their findings were presented last week at the International Conference on Computer Graphics and Interactive Techniques in Los Angeles. A copy of the research paper can be found on their website.

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Claire Trageser

Investigative Reporter

As a member of the KPBS investigative team, my job is to hold the powerful in San Diego County accountable. I've done in-depth investigations on political campaigns, police officer misconduct and neighborhood quality of life issues.

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