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I just don't get it. Isn't snow just another form of water? Also are all ices transparent or do they go white after a certain temperature?

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marked as duplicate by AccidentalFourierTransform, Jon Custer, John Rennie thermodynamics Feb 10 '17 at 8:19

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That's same for cloud, fog, wave splash and so on. Because of tiny size (but in large number) and irregular appearance, reflection and refraction occur in an irregular manner so the light is scattered randomly so that every images and colors mixed together. As a result, it looks white. By the way, under thick clouds, they look dark because all the light from the top has scattered away. Under microscope, snow flakes (ice crystal aggregate in fractal way) look crystal clear.

enter image description here

Photo credit goes to Henry David Thoreau:

  1. snowcrystals.com
  2. photos' link
  3. Method of illumination is mentioned at the end of this link.
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    $\begingroup$ Given this, could a group of snowflakes cause enough create a rainbow? :D $\endgroup$ – Anoplexian Feb 9 '17 at 15:55
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    $\begingroup$ @Anoplexian No, rainbows rely on the relative uniformity of the liquid drops to scatter light consistently across the curcular arcs of relative angle to the sun and viewer. But small ice crystals can create a similar effect. $\endgroup$ – MooseBoys Feb 9 '17 at 16:04
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    $\begingroup$ It should be noted that, because they scatter light, they only look white when most of the light hitting them is white. If the sky were red the snow would look red as well. $\endgroup$ – Dave Feb 9 '17 at 17:47
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    $\begingroup$ @Dave This property is true of most things that we attribute a color to. A white wall will also only appear white if the light hitting the wall is mostly white. It is also not the color of the sky that determines the color of the clouds. The clear sky is blue (due to Rayleigh scattering), but the clouds are still white because the direct sun light is white. $\endgroup$ – jkej Feb 9 '17 at 19:00
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    $\begingroup$ @Anoplexian I suspect the slight rainbowish hues you can see in these photos is owing to the wavelength dependence of the Fresnel equations describing the angled facets of the crystals, and the fact that different facets present different angles. There is probably some Fabry-Perot etalon effects and maybe even stress birefringence effects (the lighting for these micrographs is probably polarized). $\endgroup$ – WetSavannaAnimal Feb 9 '17 at 23:35
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Snow is simply a random collection of snowflakes and bits of irregularly shapen bits of ice. Each of these is clear, but a small fraction of the light incident on each clear entity is reflected and scattered. The fraction is of the order of 2%.

Light passing through snow encounters huge numbers of these randomly oriented interfaces. So a large fraction of it is scattered. The wavefronts of the incident waves are completely randomized by this scattering, so the scattering can no longer form images. The same goes for any light that passes through the snow: its wavefront is highly randomized and cannot form images.

The scattering happens roughly equally to all visible wavelengths, which is why we see white, diffuse light from snow when it is lit by a broadband source like the Sun.

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It isn't white. You perceive it to be white because it is clear and it is reflecting the full spectrum of light applied to it.

As for why snow appears white and, say, raindrops do not, the answer lies in the crystalline and faceted nature of snow. Consider a clear ice cube which, when crushed, appears white.

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    $\begingroup$ Isn't anything that reflects the full spectrum considered as white? $\endgroup$ – Huzo Feb 9 '17 at 14:05
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    $\begingroup$ Isn't that what "white" means? In other words, are there any white things whose whiteness is not for exactly this reason? $\endgroup$ – Henning Makholm Feb 9 '17 at 16:28
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    $\begingroup$ @HenningMakholm you could have something that just emits (through reflection, or as a direct source) just red, green and blue, in order to stimulate the rods in your eye to make you believe you are seeing white. In fact, you are looking at a device that does that, right now $\endgroup$ – Baldrickk Feb 9 '17 at 17:02
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    $\begingroup$ @Baldrickk: Sure, but I'm not sure I would say that device "is white" itself. $\endgroup$ – Henning Makholm Feb 9 '17 at 17:15
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    $\begingroup$ @Baldrickk: I don't think that is relevant for when a thing is white. A white object is one that reflects the ambient illumination at whatever spectrum that ambient illumination has. $\endgroup$ – Henning Makholm Feb 9 '17 at 17:24

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