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• To make a rainbow, you need three ingredients: sunlight, water, and you.

• Sunlight, as you probably know, consists of all of the colors in the visible spectrum,

• as well as a bunch of wavelengths of light that we can’t see.

• And when light travels from one medium -- like air -- to another, denser medium -- like water

• -- it slows down, and exits the new medium at a different angle than it entered. This

• is called refraction.

• In the case of water, light can enter a droplet, bounce off its inner surface, like a mirror,

• and then exit at sharp angle.

• And because each color has a different wavelength, theyre each slowed to a different degree

• and refracted at a different angle.

• So red light will exit the drop at 42 degrees from the angle at which the sunlight entered.

• But blue light, near the opposite end of the spectrum, will exit at 40 degrees, with the

• other colors somewhere in between.

• The combined effect of this differently refracted light scatters the colors so you can see them

• individuallyROYGBIV.

• And this is also where you enter the equation, because the conditions have to be just right.

• Rainbows only happen when the sunlight is coming from behind you and is low in the sky.

• As the sunlight shines into a curtain of raindrops in the air in front of you, only one color

• from each droplet will refract at the exact angle necessary to directly reach your eye.

• So in one part of the sky, all the raindrops will bounce red light into your eye. All the

• other colors from those particular droplets will scatter either too high, too low, or

• too far to either side for you to see them.

• But just a few degrees away in the sky, the blue light bouncing out of those raindrops

• will be the ones to reach you.

• With all those droplets refracting only a certain wavelength of light that hits your

• eye, together they create the illusion of a rainbow.

• So what creates thebowin a rainbow?

• Well, rainbows actually form in a full circle in front of you, at an angle of 40 to 42 degrees

• from your line of vision.

• This means youll always be at the center of any rainbow you see! Which is kind of a

• nice thought.

• But it also means that the Earth is going to block the lower half of the rainbow, so

• you typically only see the upper arc.

• However, some extremely lucky skydivers, pilots, and mountaineers have gotten high enough above

• the horizon precisely in the right conditions to see a full circular rainbow. It DOES exist.

• But I am perfectly happy just seeing half of the rainbow and staying right here on the

• ground, thank you very much.

• Thanks for asking, and thanks especially to our Subbable subscribers who get these videos

• a little bit early, for subscribing. Thank you! If you want to get these videos early,

• you can go to subbable.com/scishow.

• If you have a quick question for us, you can let us know on Facebook and Twitter or in

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• and subscribe!

To make a rainbow, you need three ingredients: sunlight, water, and you.

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# How Do Rainbows Form?

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Hhart Budha posted on 2014/06/17
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