Why is Snow White? Exploring the Physics of Light Reflection

[Coolcrab]

So I was wondering why snow is white as water and ice are not. I looked around on the internet and found a few explanations (which didn't all match, so I decided to post what I believe it to be now, and you guys can tell me if I am right or not :P)

So light reflects off surfaces, you can see this with ice at the front and back, and the same goes for snowflakes, which are small icecubes. So all the light gets reflected back and forth by all the snowflakes which are randomly arranged and then scattered back out of the snow into your eye. (I think the scattering is diffuse?)

When you compress the snow, the flakes become less randomly arranged and more tightly packed. So the light can reflect less easily and flow trough more. This makes it a bit more transparent.

Am I right?

Also, this is my first post so hi all. I am Alex a 2nd year physics student. And I love to find explanations for stuff like this. (So you'll be seeing more if these type of questions)

 

[phinds]

I can't tell you why snow is white but I absolutely disagree w/ you that ice is NOT white.

SOME ice is not white, and some is. "Black ice" for example has no hint of white but my refrigerator ice maker's ice is white --- not as white as snow but not the least bit transparent/clear

 

[Coolcrab]

Yea but isn't that because of the same reason?
Ice that's frozen unevenly will have lots of impurities and hence more faced to reflect light off.

 

[phinds]

Yea but isn't that because of the same reason?
Ice that's frozen unevenly will have lots of impurities and hence more faced to reflect light off.

Your statement was that ice is not white. That's what I was commenting on. There was no "yes but" in the original statement.

 

[Coolcrab]

Thats because I don't agree with you, it can be white when impure but pure ice is translucent and blueish.
Glass isn't white, but if crack it and look at the cracks then those are. It has to do with how even the crystal is.

 

[phinds]

Thats because I don't agree with you, it can be white when impure but pure ice is translucent and blueish.
Glass isn't white, but if crack it and look at the cracks then those are. It has to do with how even the crystal is.

Yes, that is exactly my point. Your original statement was that ice is not white. NOW you say that it CAN be white.

My point is simply that poorly stated questions can be a reflection of poor or incomplete thought processes.

We are arguing about very little here. Make your questions more correct, is all I'm saying.

 

[Drakkith]

Your original post is pretty much correct. The irregular surface of the snow scatters and reflects the light, so you end up with the whole spectrum of sunlight, which is white, coming back at you. Ice and water are not white because, when they are smooth and free of impurities, the light is transmitted through. However, if the angle of the light is high enough it is reflected instead, allowing you to see reflections of yourself in water or ice as long as they are smooth enough and relatively free of impurities.

Ice cubes are sometimes smooth enough to transmit light and sometimes not, thus giving some of them a clear shiny look, and some of them a white frosty look.

 

[Bobbywhy]

Snow is normally white. Ice, however, forms in nature in lots of colors!
See:
http://www.dailycognition.com/index...-of-color-striped-icebergs-in-antarctic.html/

http://en.wikipedia.org/wiki/Blue_iceberg

 

[Coolcrab]

However, if the angle of the light is high enough it is reflected instead, allowing you to see reflections of yourself in water or ice as long as they are smooth enough and relatively free of impurities.

Yea, that's the brewster angle, but that's not what happens to snowflakes right? In the way that its not a reflection, but rather a whole bunch of randomly scatted light

Also, does this same phenomenon make clouds white? Because it does seem to be the same effect. The only difference being that they become gray instead of blue when they are rainclouds, larger and thicker clouds. But is that just because they absorb a lot of the light?

 

[Drakkith]

Yea, that's the brewster angle, but that's not what happens to snowflakes right? In the way that its not a reflection, but rather a whole bunch of randomly scatted light

I believe the scattering is due to a combination of refraction and reflection. But yes, the reflection off a smooth surface is different from the snowflakes.

Also, does this same phenomenon make clouds white? Because it does seem to be the same effect. The only difference being that they become gray instead of blue when they are rainclouds, larger and thicker clouds. But is that just because they absorb a lot of the light?

Try this section of the article on clouds: http://en.wikipedia.org/wiki/Cloud#Coloration

 

[NascentOxygen]

I can't tell you why snow is white but I absolutely disagree w/ you that ice is NOT white.

SOME ice is not white, and some is. "Black ice" for example has no hint of white but my refrigerator ice maker's ice is white --- not as white as snow but not the least bit transparent/clear

I believe if you got rid of the included gas, and had just ice, pure ice, and nothing but ice, you'd show that ice really is transparent.

 

[Coolcrab]

Uhu, and that's what we are talking about, the pure stuff, not mixtures.

 

[nasu]

So I was wondering why snow is white as water and ice are not.

It may that the definition of "white" is a little fuzzy.
If we call white something that reflects equally well all visible frequencies, then snow, water and ice are all white.
The transparency of an object should not be confounded with its "color".
If you shine white light on ice or water, white light is reflected back. Not a lot of it but the spectral response is relatively flat (compared with the case you shine white light on blue, transparent glass, for example).
The difference is in the amount of reflected light and the quality of reflection (specular versus diffuse).
In common language we call "white" something like snow but for water we would rather say it's clear or transparent (and not white). However transparency and color are quite distinct properties.
If you grind glass in a fine powder it becomes "white". Same thing happens with ice. Of course, the snow flakes are not crushed ice but ice crystals grown individually in very interesting shapes.
On the other hand, if ice were not "white" to start with, then snow would be still shiny bright maybe, but probably it won't be white.

 

[Andy Resnick]

So I was wondering why snow is white as water and ice are not.<snip>

As Drakkith points out, the reason is scattering: snow permits multiple scattering, while solid ice and liquid water generally only have single scattering. It's worth pointing out that snow only looks white in the visible; in the infrared it's black- that's because water is very transparent in the visible but opaque in the infrared.