Color Vision, Diet Advice and How Rainbows Work: a 3 minute (or so) presentation

I was about to post my FameLab presentation on human evolution when I realised I had never blogged my video on how rainbows work.

I took part in the preliminaries of the Greek FameLab competition in 2010 and made it to the finals, but never got the chance to compete because the Greek Army wouldn’t let me out of boot camp. FameLab is an international science communication competition. The participants are supposed to present a scientific subject in a clear, concise, and entertaining manner, in under 3 minutes.
I had the opportunity, along with the rest of the Greek finalists, to take part in a workshop on science communication and media skills. As part of the workshop, we were supposed to prepare a 3 minute presentation on one of the following subjects:
1. What makes pop corn pop?
2. What causes a rainbow?
3. Why do leaves change colour in autumn?
4. Why do I feel dizzy when I spin?
5. What are stem cells?
6. Why do some people have brown eyes – or blue?
7. What is the difference between bacteria and viruses?

None of these subjects are particularly fascinating to me. In the end, I picked rainbows, hoping to talk about colors and vision and xkcd’s fascinating color survey. Unfortunately, it turns out there’s only so much you can fit into 3 minutes, all while trying to explain a phenomenon that is not, in fact, as simple as saying “refraction”. Thanks to the internet, this can now be remedied. Here’s the text of the presentation I wanted to give, followed by the video of the actual one, right after the jump.


So. Rainbows.
Rainbows occur whenever homosexuals fall in love. It just happens to coincide with the moments right after rainfall.
You can actually force two gay people to fall in love by watering your garden.
Because it’s their symbol…? No? Okay.

Imagine you’re sitting with the sunset at your back and you’re watching some passing stormclouds. When the sunlight meets the waterdrops in the lower atmosphere, two things can happen:
First, nothing. It just goes right through.
Second, refraction.
Refraction is what happens when you put a straw in a glass of water: it looks crooked. Imagine that the light from the sun is the straw. It enters the waterdrop, gets bent, bounces off the rear edge of the drop, gets bent again, and comes back out towards us.

Now we’re going to talk about colors.
Thanks to Newton we know that white light, sunlight, is actually comprised of all the colors of the spectrum, or all the colors of the rainbow. Red, orange, yellow, green, blue, indigo and violet. Color is not a property of an object, it’s just a construct of the brain. A red apple doesn’t emit red light, it just absorbs all the frequencies of light except the one we call red. In the end, colors are just names that we humans have given to frequencies of light.
The reason we evolved colored vision is that, at some point, primates switched from nighttime to daytime activity and began consuming fruits and leaves. Color vision is extremely useful when you need to tell between fresh and bad fruit.
You may have noticed that there aren’t many naturally occuring blue foods. That’s why it isn’t a color we associate with edible products. I mean, seriously: blue cheese. Out of all the colors of the spectrum, blue is the only appetite suppressant. In fact, some weight loss plans suggest serving your food on a blue plate or installing a blue light in your fridge.
… it worked for me.

Sight is, after all, a huge part of the satisfaction we get from food. If I describe a juicy bacon hamburger with onions, tomato, lettuce, a thick patty and melted cheese, you’re not thinking about the taste… you’re actually picturing it!
(By the way, did you know that our eyes have a blind spot? It’s because the optical nerves are in front of the retina, and they have to go through it to reach the brain. If you mark an X on a piece of paper, close one eye and hold it at just the right spot, you can make it disappear. Try it! It’s awesome!)

Anyways. Rainbows. Remember refraction?

Image from How Stuff Works’ explanation, which you might prefer

The angle of refraction depends on the wavelength of the light wave. When sunlight enters the water drop, different colors get refracted by different amounts. Red, which has a long wavelength gets refracted by just a tiny bit. It bends a little going in, hits the opposite side, and bends a little bit backwards on its way out (… see what I did there?). It ends up at a larger angle than it had going in, and comes straight into our eyes. Blue, on the other hand, has a shorter wavelength so it bends a lot more. Since it gets refracted twice, it emerges at an angle almost equal to the one it had on entering. You would have to be much taller for it to reach your eyes. Either that, or the waterdrop would have to be much lower. That’s why the rainbow starts with red, when you would expect it to start with blue.

… And that’s how rainbows work.
Pretty much.
Accompanied by a lot of tangentially related information.

Here’s the video:

2 Responses to “Color Vision, Diet Advice and How Rainbows Work: a 3 minute (or so) presentation”

  1. Kostas Karpouzis Says:

    You rule! You should consider a career doing that 😀

  2. dukeoglue Says:

    I’m sure that will work out for me