why do polar bears appear black in ultraviolet light?
Despite what our eyes tell us, a polar bear's fur is not white. Each hair shaft is pigment-free and transparent with a hollow core.
Polar bears look white because the hollow core scatters and reflects visible light, much like ice and snow does.
When photographed with film sensitive to ultraviolet light, polar bears appear black.
Early speculation over this discrepancy produced a theory, now widely repeated as fact, that polar bear hair acts like a fiber optic guide to conduct ultraviolet light to the skin.
In 1998, Daniel W. Koon, a physicist at St. Lawrence University in Canton, New York, decided to actually test whether or not polar bear hair could efficiently conduct ultraviolet light.
Koon and a graduate assistant, Reid Hutchins, obtained polar bear hair from the Seneca Park Zoo in Rochester. Their experiments showed that a one-fifth inch strand of polar bear hair was able to conduct less than a thousandth of a percent of the applied ultraviolet light. With such a high loss rate, meaningful amounts of ultraviolet light cannot be reaching a polar bear's skin.
Instead, Koon believes the ultraviolet light is absorbed by the keratin making up the hair.
Polar bears look white because the hollow core scatters and reflects visible light, much like ice and snow does.
When photographed with film sensitive to ultraviolet light, polar bears appear black.
Early speculation over this discrepancy produced a theory, now widely repeated as fact, that polar bear hair acts like a fiber optic guide to conduct ultraviolet light to the skin.
In 1998, Daniel W. Koon, a physicist at St. Lawrence University in Canton, New York, decided to actually test whether or not polar bear hair could efficiently conduct ultraviolet light.
Koon and a graduate assistant, Reid Hutchins, obtained polar bear hair from the Seneca Park Zoo in Rochester. Their experiments showed that a one-fifth inch strand of polar bear hair was able to conduct less than a thousandth of a percent of the applied ultraviolet light. With such a high loss rate, meaningful amounts of ultraviolet light cannot be reaching a polar bear's skin.
Instead, Koon believes the ultraviolet light is absorbed by the keratin making up the hair.
In 1979, three polar bears at the San Diego Zoo turned green. Scientists discovered that colonies of algae were growing in the bears' hollow hair shafts.
Although the algae in no way harmed the animals, zoo veterinarian Phillip Robinson restored the bears' white fur by killing the algae with a salt solution.
The fur on a polar bear cub is whiter than that of adult bears. In older bears, fur colors range from white to almost yellow.
Hybrid cubs born to captive polar bears and their close relative, the brown bear, are white at birth but later turn blue-brown or yellow-white.
A polar bear is so well-insulated that it experiences almost no heat loss. In addition to its insulating fur, the bear's blubber layer can measure 4.5 inches thick.
So effective is the polar bear's insulation that adult males quickly overheat when they run.
Because polar bears give off no detectable heat, they do not show up in infrared photographs. (Infrared film measures heat.) When a scientist attempted to photograph a bear with such film, he produced a print with a single spot--the puff of air caused by the animal's breath.
Although the algae in no way harmed the animals, zoo veterinarian Phillip Robinson restored the bears' white fur by killing the algae with a salt solution.
The fur on a polar bear cub is whiter than that of adult bears. In older bears, fur colors range from white to almost yellow.
Hybrid cubs born to captive polar bears and their close relative, the brown bear, are white at birth but later turn blue-brown or yellow-white.
A polar bear is so well-insulated that it experiences almost no heat loss. In addition to its insulating fur, the bear's blubber layer can measure 4.5 inches thick.
So effective is the polar bear's insulation that adult males quickly overheat when they run.
Because polar bears give off no detectable heat, they do not show up in infrared photographs. (Infrared film measures heat.) When a scientist attempted to photograph a bear with such film, he produced a print with a single spot--the puff of air caused by the animal's breath.
I started an answer, but found myself starting to make things up. 
I'll have to give that an I Don't Know. 
I'll have to give that an I Don't Know.
Well, I read a few in google and guess what..I don't think they do either!! 
I've never seen a polar bear in an old western !
So, does that mean I collect, or have to pay, 5 cents?
Yes it does.
That's what I came up with, but wanted someone to double check.
Puppy Raiser Wins - I had to learn this yesterday from a six year old and I spent 7 years in the Arctic. Mory
Moryquote:
Originally posted by Puppy Raiser:
Snow flakes don't have skin, and ice is clear.
THAT'S FUNNY.
quote:
Originally posted by Puppy Raiser:
Why doesn't snow turn green when it falls on green grass?
That's also a good one.
quote:
Originally posted by MORY:
and I spent 7 years in the Arctic.
My oh my. You must have some interesting stories.
(that's a .jpg)
Yes, and I can see it and it is cute! Love those bvds
quote:
Originally posted by Mrs.M:
kind of yellowish
No nickel for your piggy bank.
Oh, darn.
Try this and key in "Polar Bear color":
http://www.google.com/advanced_search?hl=en_extra
Send nickel via
http://www.google.com/advanced_search?hl=en_extra
Send nickel via
Can I send it collect?
