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What Would a Rainbow Look Like on Tatooine?

If the double rainbow guy — you know, this guy — ever visited Luke Skywalker’s home world while the climate was unusually wet, his head would explode. Why? Because according to entertainer and science educator xkcd, a planet like Tatooine, which orbits a binary star system, would have quadruple rainbows! 

Whoooooaaaaaaa, now that’s bright and vivid, young Jedi! 

Somebody by the name of Raga recently posed the question: “Since rainbows are caused by the refraction of the sunlight by tiny droplets of rainwater, what would [a] rainbow look like on Earth if we had two suns like Tatooine?” And xkcd broke down all of the science that led him to the answer of quadruple rainbows.

On Earth, a rainbow is caused by light coming from the Sun that gets refracted by water droplets in the atmosphere. This refraction occurs because as light transfers from air to a denser medium, water, it slows down and exits the denser medium at a new angle relative to the angle at which it entered. This causes it to break up into its constituent wavelengths (different colors) due to their varying speeds. (SciShow explains this concept very well.)

xkcd notes that rainbows on Earth are actually already double rainbows, or even triple or quadruple or some other number of rainbows because “Rainbows are formed by light bouncing around in raindrops, and the different bows are formed by different paths the light can take.”


But Tatooine has two stars, and xkcd points out that it’s probably a circumbinary planet because of the way the stars appear in its sky (That hero shot from A New Hope though). This would mean that Tatooine orbits around a tight, core pair of suns.

Tatooine-Rainbow-Graphic-Two-05252016Above: xkcd’s Illustration shows Tatooine’s likely orbit (left).


Based on that theory, xkcd concludes that Tatooine’s two stars would orbit closely to each other in the sky, and would thusly create two overlapping rainbows in its atmosphere. He also concludes that the rainbows wouldn’t be very far apart from each other because if they were, that would mean the stars in Tatooine’s sky would have to be far apart too; and if that were the case, then Tatooine would be in an unstable orbit around them, and would either “get flung out of the system” or crash into one of the stars. And for a planet with that many rainbows, that just doesn’t seem right.

What does seem right about Tatooine’s theoretical quadruple rainbow? Give us your thoughts in the comments below!

Images: Lucasfilm, xkcd 

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