Rebecca Vineyard
May 28, 2016 7:33 am
Lucasfilm

Chances are, you’ve seen a rainbow before — you may have even encountered double ones. Actually, according to science educator and entertainer xkcd, all rainbows on Earth are double; conditions don’t always allow you to see the second one — the clouds have to be just right.

xkcd

While doubles are pretty impressive, though, they’ve got nothing on quadruple rainbows. Yep, those are a thing — or at least, they could be, if we lived on Tatooine.

That’s right: we do mean the arid, desert home of Luke Skywalker as depicted in Star Wars: A New Hope.

According to Nerdist, xkcd received a question by someone named Raga, who asked: “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?”

Xkcd answered that Tatooine would have quadruple rainbows, and explained the science behind that answer. Essentially, the sun’s light gets refracted by water droplets in the atmosphere as that light travels from air to the water, which is more dense. Due to this density, the light slows and leaves the water from a new angle; varying speeds actually cause the light to produce the colors you see in a rainbow.

However, on a planet like Tatooine, which has two suns — as is evidenced by one of the most famous shots in the Star Wars franchise — and likely orbits around them both, the two suns orbiting closely would probably cause overlapping rainbows within the planet’s atmosphere.

Lucasfilm

Xkcd even explains why the two stars are likely close to one another (basically, if they weren’t, Tatooine’s orbit would become unstable and the planet would either get thrown right out of the system, or collide with stars). Luckily, that won’t happen- mostly because Tatooine isn’t real. (However, there are planets out there somewhere with two suns.)

Don’t be too heartbroken about Earth’s lack of quadruple rainbows, though: according to xkcd, light can bounce around in strange ways and cause more than two visible rainbows to appear, sometimes. One instance of this is a quadruple rainbow that was photographed by Amanda Curtis in Long Island, NY last year.

Many people thought it was photoshopped, but the extra rainbows were actually produced by a body of water, which created a reflective surface for the sun’s light to bounce off — and in turn, created a second pair of rainbows. So, even if Tatooine isn’t real, quadruple rainbows are — they’re just as rare as they are beautiful.

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