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Polar Bear Fur: Newsletter Challenge (07/05/05)

Posted July 05, 2005 7:00 AM

The question as it appears in the 07/05 edition of Specs & Techs from GlobalSpec:

Here in the Northeast region of the U.S., summer is upon us in full force - meaning record high temps, oppressive humidity and envious thoughts about the inhabitants of the Arctic region. While on this train of thought, what color is polar bear fur?

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The Engineer
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#1

I know that it's not white

07/05/2005 10:20 AM

I forget what the explanation is for why it appears white though.

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#2
In reply to #1

Re:I know that it's not white

07/05/2005 11:04 AM

Polar Bear Fur is transparent, and reflects visual light, also just fyi, polar bear skin is black

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The Engineer
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#3
In reply to #2

Re:I know that it's not white

07/05/2005 11:10 AM

That doesn't seem right, if a material is transparent, it doesn't reflect visual light.

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#4
In reply to #3

Re:I know that it's not white

07/05/2005 11:32 AM

From what I know, the hair "shaft" for lake of a better word is pigment free and hollow, thus the light is hollow hair shaft scatters and reflects the visual light much like snow and ice does.

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The Engineer
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#5
In reply to #4

Re:I know that it's not white

07/05/2005 12:45 PM

Scattering sounds more likely. That makes for a pretty efficient system if you think about it. The transparent hair lets the light pass through, the black skin absorbs the light and warms the bear, even as the scattering of every color makes it appear white. I wonder what function having the hair be hollow serves.

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#6
In reply to #5

Re:I know that it's not white

07/05/2005 1:27 PM

I seem to remember it has an insulating affect.

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#8
In reply to #6

Re:I know that it's not white

07/06/2005 2:40 AM

In fact I read somewhere that scientists tried to track Polar bears using Infared cameras, and the bears lose so little heat they did not appear on camera

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#12
In reply to #8

Re:I know that it's not white

08/03/2005 2:39 PM

"In fact I read somewhere that scientists tried to track Polar bears using Infared cameras, and the bears lose so little heat they did not appear on camera"

^ thats wicked cool!... 'stealth technology' haha

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#7

Polar bears

07/06/2005 1:46 AM

I recall having read that the hair on the bear's fur is transparent and hollow and that the air in the hollows reflect/refract light thus preventing light in our visible spectrum from being absorbed by the coat. This makes the bear appear white.

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Guru
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#10
In reply to #7

Re:Polar bears

07/06/2005 4:25 AM

This is correct, also, their skin is black to absorb heat.

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#9

Polar bear fur

07/06/2005 3:58 AM

Differently from other arctic mammalians, the polar bear (Thalarctos/Ursus maritimus)does not considerably change in summer the color of his fur: the white shades slightly into yellow-gold. As well known, the hair is not filled with white pigment, but it is hollow as the hairs of an elderly person. Of course, the color as it appears to us depends on the spectrum of the reflected light. Moreover, recently the model "polar bear hair as optical fiber" proved to be groundless.

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#11

And the Answer is...

07/12/2005 12:50 PM

As written in the 7/12 issue of Specs & Techs from GlobalSpec:

Polar bear fur lacks any pigment and appears transparent under a microscope. The inherent porosity in the polar bear fur scatters light making their transparent hair appear white. Similar effects can be seen in synthetic insulation and advanced ceramic products. Ceramics like aluminum oxide are normally white because they are made from a powder and some porosity is retained after densification. If aluminum oxide is made fully dense by hot pressing or doping, then it becomes transparent.

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