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Can You Reach The End Of A Rainbow?

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Channel: BrainStuff - HowStuffWorks
Categories: Physics   |   Science  
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The end of the rainbow may be the best place to raid a leprechaun stash, but it proves a strangely difficult destination to reach. Brainstuff explains why you can’t get there, and why there really isn’t even a a “there” there.

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OK, so you have this amazing idea to start your own business: A licorice-themed food truck. Genius, right? But the bank turned you down, and your Kickstarter campaign failed to fund.

FORTUNATELY, you know where you might be able to find a large stash of gold… if you can ONLY get to the end of this rainbow you’ve been following for six hours.

But is it actually possible to get to the end of a rainbow? And if so, what will you find when you get there?

Let’s start with the bad news: Leprechauns are liars. You cannot reach the end of the rainbow. If you were to mark on a map the place where the rainbow seems to meet the land, and then travel to that location, you would not be standing inside a glorious pillar of colors. There would be nothing there, except probably the fresh smell of a recent rain shower.

To understand why this is, we need to look at how rainbows form. Rainbows are created when sunlight reflects and refracts through water droplets suspended in the air, on the opposite side of you from the sun. Those water droplets act like both a mirror and a prism.

Like a mirror, they reflect the sunlight back toward you. But like a prism, they also bend and disperse the light.

This is because rays of light shining through the air change speed when they enter a different medium -- for example, water. This sudden change in speed bends the trajectory of the light, and disperses white light into the whole Roy G. Biv spectrum.

The reason you see a nice, ordered gradient of colors within a rainbow, going from red to violet, is because this refraction bends each of the different colors of light at a slightly different angle.

So, for example, red light bends at 42 degrees, violet light bends at 40 degrees, and all the other colors are somewhere in between.

So let’s find a rainbow. To do this, you need to locate your anti-solar point. Your anti-solar point is the point in space 180 degrees -- or exactly opposite -- from the sun.

A simple way to find this is to go outside and look for the shadow of your own head. Now imagine drawing a straight line in 3 dimensions from the sun through your head to the shadow of your head.

Now look up: If there is a rainbow to be seen, you will find it by facing away from the sun and looking for an arc 42 degrees above that line from the sun to your anti-solar point.

Notice that the apparent location of your rainbow depends on three things: Where the sun is, where the water droplets are, and where your eyes are. Change any one of those variables and you’ll see a different rainbow -- or none at all.

So no matter where you see your rainbow, if you try to walk out to meet it, you’ll be changing the variable of your own position, and you could be walking forever – or at least until your rainbow disappears.

Trying to find the end of a rainbow is sort of like trying to walk to the end of your own shadow. Somebody else could stand at the apparent end of your rainbow, but you will never, ever reach this location yourself.

But here’s another thing: A rainbow isn’t actually a bow. Rainbows are circular. Usually, when you’re standing on the ground, most of the rainbow is blocked by the horizon. In rare cases, like if you’re in an airplane or something, you’ll be able to see the entire rainbow —err, rainhoop? — rainloop? — rainhole? — a round, spectacular beauty.

But there’s an obvious take-away from this: It doesn’t actually meet the ground anywhere. There’s just the altitude where you can’t see it anymore.

Despite all this science that is quite well understood, you’ll find people on the Internet swearing up and down that they’ve found the end of a rainbow. Not sure what’s up with that.


360 degree rainbow photo:


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