Mystery 1: Is polar bear fur transparent?

by Stephanie Chasteen on January 18, 2008

polar-bear.jpgThe answer seems to be yes! Even though polar bears are white, their hair is actually colorless. I found this out by looking at a great site, Everyday Mysteries, run by the Library of Congress. You can browse tons of questions, and their interesting science answers, compiled by the expert reference librarians at the Library of Congress. Aren’t librarians great?

Here’s a link to the polar bear posting itself. The reason we can’t see through the “transparent” hair directly to the polar bear’s skin (eek! naked polar bear!) is that the hairs are hollow. The air inside the hollow space in the hair bounces the white light from the air back to our eye, sort of like millions of tiny mirrors tilted at tons of different angles. The result is that we see a white bear.

In that same LOC posting is an interesting tidbit — bears at some zoos were turning green! Why? There was algae growing inside the hairs… so those hollow spaces weren’t reflecting white light anymore, but green light. How embarrassing for the poor polar bear.

Note that polar bear hair is NOT a fiber optic. You can see my earlier posting about that.

{ 4 comments… read them below or add one }

tony July 9, 2008 at 10:00 pm

so are you saying that air reflects white light? i still don’t understand how a polar bear’s black skin is supposed to absorb light and heat up the bear. it seems to be like having your cake and eating it too. the hair somehow reflects light, making the bear look white, but the light also manages to get to the black skin even though it was reflected by the hair. please help me understand this.

sciencegeekgirl July 9, 2008 at 10:39 pm

Not quite. The hollow polar bear hairs “scatter” the white light. What that means is that when white light hits the hollow hair, it bounces off in all directions. Think of a foggy day. The fog itself is colorless (it’s just a bunch of water droplets), but when you look at it, it looks kind of white. That’s because as light (of any color) hits the fog, the little water droplets act like a bunch of mirrors skewed at crazy angles, and just reflect the light in all different directions. The eye sees that scattered light as white.

So, that takes care of your first question, whether air reflects white light. Now for your second qustion, about a polar bear’s black skin. The polar bear’s black skin does NOT absorb light and heat up the bear, that is NOT how a bear keeps warm. Check out the earlier posting about how polar bear hair is not a fiber optic to see the debunking of that myth. The white light *can’t* get to the polar bear’s skin, for the reasons I talk about above. The polar bear stays warm because the hairs are hollow, and those hollow hairs insulate the bear like a big down jacket.

Let me know if that helps at all! I know the idea of “scattering” is a bit weird.

tony July 9, 2008 at 10:46 pm

I was at sea world a few weeks ago, and they really tried to pound it into our heads that the polar bear’s have black skin under their white fur to help absorb heat. i knew immediately it was wrong because something cant reflect light (the condition for being white) and absorb it at the same time. but that still leaves light outside of the spectrum that we can normally see. what if the bear’s fur lets in ultraviolet or infrared light? well apparently it doesn’t. so then why is a polar bear’s skin black? my guess is that it is black because it is descended from a bear that had black skin.

Curtis February 24, 2009 at 5:10 pm

um,im doing a scince project, with the prompt, explain the color of the polar bear, by natural selection, could anyone send me help?please,
send to, curtsciencehw@yahoo.com
if you will

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