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  #1201  
Old 11.08.2011, 22:02
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Re: Ask a Scientist

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Why is meltwater from glaciers and snowy peaks distinctively pale blue in colour?
economisto is right. The point is that any small particles and even molecules scatter light. They scatter light with a small wavelength (blue) more than light with a long wavelength (red). So glaciers are blue for the same reason that the sky is blue. The blue part of the light from the sun is scattered more efficiently.
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  #1202  
Old 11.08.2011, 22:17
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Re: Ask a Scientist

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It's the same cloud, with totally different appearances - under it, it looks dark (most of the light is being absorbed); in it, it's getting progressively lighter as you rise up through it (less and less absorption); above it, it's brilliant white (no absorption, lots of reflection of the sunlight striking it).
Nice explanation. All I'd add is that the water droplets don't absorb light. They only scatter it. The cloud looks black from below because all the light has already been scattered higher up. As stated, it looks really bright from above, in consequence it looks really dark from below. What goes up cannot go down...

Last edited by FrankZappa; 11.08.2011 at 22:17. Reason: fat fingers
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  #1203  
Old 11.08.2011, 22:19
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Re: Ask a Scientist

It is blue because both water and ice are composed of H and O, the bond stretch of which absorbs light at the red end of the visible spectrum.
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  #1204  
Old 11.08.2011, 23:01
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Re: Ask a Scientist

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It is blue because both water and ice are composed of H and O, the bond stretch of which absorbs light at the red end of the visible spectrum.
Wrong. It's nothing to do with bonds. Any small particles scatter blue light more than red. Rayleigh theory.
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  #1205  
Old 12.08.2011, 07:57
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Re: Ask a Scientist

Apparently we are both wrong and both right: according to Wikipedia it's both selective absorption AND scattering of light:

Wikipedia reference-linkColor_of_water

If you don't want to follow the link, here's the first paragraph: "The blue tint of water is an intrinsic property and is caused by selective absorption and scattering of white light. Impurities dissolved or suspended in water may give water different colored appearances."

It goes on to confirm what I said: " The water molecule has three fundamental modes of vibration. There are two O-H stretching vibrations which occur at ca. 3500 cm−1 and an H-O-H bending vibration at ca. 1640 cm−1. Absorption due to these vibrations occurs in the infrared region of the spectrum. The observed absorption in the visible spectrum is due mainly to the fourth harmonic frequency (third overtone) of the O-H bond-stretching vibrations. 4×3500=14000; 14000 cm−1 is equivalent to a wavelength of ca. 715 nm.[1] The actual absorption maximum occurs at 698 nm.[2]
Absorption intensity decreases markedly with each successive overtone, resulting in very weak absorption for the third overtone. For this reason, the pipe* needs to have a length of a metre or more and the water must be purified by microfiltration to remove any particles that could produce Rayleigh scattering."

* Note: it refers to an experiment to demonstrate the intrinsic color of water.
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  #1206  
Old 12.08.2011, 08:19
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Re: Ask a Scientist

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Both of you have nicely explained why air or pure water are blue except the question was why meltwater from glaciers is pale blue...and that was nicely answered by economisto (due to the colour of the ground up bits of rock in it). If our mountains were predominantly made of red rock the water would look red. As can be seen in other parts of the world.
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  #1207  
Old 12.08.2011, 11:41
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Re: Ask a Scientist

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Both of you have nicely explained why air or pure water are blue except the question was why meltwater from glaciers is pale blue...and that was nicely answered by economisto (due to the colour of the ground up bits of rock in it). If our mountains were predominantly made of red rock the water would look red. As can be seen in other parts of the world.
Well....basically if you have a cloud of particle of any type or colour, light will be scattered about. The bit of light that will be scattered about most/best is blue because it has the shortest wavelength (the long wavelength will go straight through (think of how radio waves with longer wavelengths like AM travel through walls better than short wave or FM radio)). So even without the colour of the particles, the colour of particulates are most likely to be more blue than any other colour. Of course, a cloud of red dust will be red because the colour of the actual particle is more relevant.
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  #1208  
Old 12.08.2011, 20:01
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Re: Ask a Scientist

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Apparently we are both wrong and both right: according to Wikipedia it's both selective absorption AND scattering of light:

Wikipedia reference-linkColor_of_water

If you don't want to follow the link, here's the first paragraph: "The blue tint of water is an intrinsic property and is caused by selective absorption and scattering of white light. Impurities dissolved or suspended in water may give water different colored appearances."

It goes on to confirm what I said: " The water molecule has three fundamental modes of vibration. There are two O-H stretching vibrations which occur at ca. 3500 cm−1 and an H-O-H bending vibration at ca. 1640 cm−1. Absorption due to these vibrations occurs in the infrared region of the spectrum. The observed absorption in the visible spectrum is due mainly to the fourth harmonic frequency (third overtone) of the O-H bond-stretching vibrations. 4×3500=14000; 14000 cm−1 is equivalent to a wavelength of ca. 715 nm.[1] The actual absorption maximum occurs at 698 nm.[2]
Absorption intensity decreases markedly with each successive overtone, resulting in very weak absorption for the third overtone. For this reason, the pipe* needs to have a length of a metre or more and the water must be purified by microfiltration to remove any particles that could produce Rayleigh scattering."

* Note: it refers to an experiment to demonstrate the intrinsic color of water.
Fair enough. I was hasty in my reply. The Wikipedia entry is excellent. After a short sulk about being wrong , I may be back with more info.
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  #1209  
Old 12.08.2011, 20:07
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Re: Ask a Scientist

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Fair enough. I was hasty in my reply. The Wikipedia entry is excellent. After a short sulk about being wrong , I may be back with more info.
Whilst you're sulking, you could also reflect on the (let's just say) "split" vote in the range of scientific opinion on the degree of absorption by clouds
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  #1210  
Old 14.08.2011, 22:18
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Re: Ask a Scientist

Here's my considered reply . Since Van de Hulst's "Scattering of light by small particles" sits on my bookshelf, I really should have got this straighter sooner.

1) Water is very slightly blue. But the colour is only visible if the light has travelled a large distance through it. Thus, glasses of water and blocks of pure ice do not look blue.
2) To see light that has travelled a long distance through water or ice, either it is in a white swimming pool, see the Wikipedia entry cited above, or it has some small particles or bubbles in it, e.g. glacier ice (bubbles) or meltwater (particles). The only function of the particles or bubbles is to scatter the light, so that it bounces around a lot, like sound in a cathedral. Their size or colour doesn't matter, in general.

My argument about very small particles or molecules (diameter less then 0.1micrometer) being bluer (due to Rayleigh scattering) is true for the sky, but not relevant for water.

In general, economisto's argument that melt water is blue because it's full of blue particles is not true, since most of the clay and silica particles in melt water are not blue.
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  #1211  
Old 17.08.2011, 01:59
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Re: Ask a Scientist

Anyone get it ?

ask-scientist-17-08-2011-01-57-40.jpg
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  #1212  
Old 17.08.2011, 02:15
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Re: Ask a Scientist

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Anyone get it ?

Attachment 31103
The slope of two small triangles is not the same. Red is 2:5 and green is 3:8. Therefore what appears to be a large triangle is not as the line bends covexly in one arrangement and concavely in the other. This is the reason why there is an extra space because there is actually more space under the "curve". So to speak.
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  #1213  
Old 17.08.2011, 02:18
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Re: Ask a Scientist

My son wants to know why I am so sure he was made with only one egg and one sperm. He came to me the other day and wanted to know if I was sure he had "only one sperm in him," which of course was long ago when he was one cell. I tried to explain that again. But seriously, for geneticists or developmental biologists - what makes sure that ONLY one sperm enters an egg? I read that there is a chemical block but then if there was a mistake (simultaneous entry), what kills a trisomy embryo?
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  #1214  
Old 17.08.2011, 02:23
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Re: Ask a Scientist

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The slope of two small triangles is not the same. Red is 2:5 and green is 3:8. Therefore what appears to be a large triangle is not as the line bends covexly in one arrangement and concavely in the other. This is the reason why there is an extra space because there is actually more space under the "curve". So to speak.
Help me out, I am not seeing the convex and concaveness. Is it an optical illusion.
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  #1215  
Old 17.08.2011, 02:59
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Re: Ask a Scientist

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Help me out, I am not seeing the convex and concaveness. Is it an optical illusion.
Look closely at the edge of the red "triangle" in the grid square directly above the gap in the bottom diagram, then look at the same part in the top - you can see that they intersect the grid lines at slightly different places.

After a bit of searching, the most in-depth explanation of it I came across is here.

Last edited by Monomix; 17.08.2011 at 03:49.
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  #1216  
Old 17.08.2011, 03:16
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Re: Ask a Scientist

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Help me out, I am not seeing the convex and concaveness. Is it an optical illusion.
The line of the "large" triangle is not actually a line. It is two segments with a slight angle difference between the two.

And yes it is meant to be an optical illusion.

The actually area under the "curve" of the top shape is 32 units and the area of the bottom shape is 33 units. If you use your middle school geometry to calculate all of the areas of the shapes contained within the main shape.
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  #1217  
Old 17.08.2011, 03:21
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Re: Ask a Scientist

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My son wants to know why I am so sure he was made with only one egg and one sperm. He came to me the other day and wanted to know if I was sure he had "only one sperm in him," which of course was long ago when he was one cell. I tried to explain that again. But seriously, for geneticists or developmental biologists - what makes sure that ONLY one sperm enters an egg? I read that there is a chemical block but then if there was a mistake (simultaneous entry), what kills a trisomy embryo?
The electro chemical reaction that blocks the entrance of an other spermatozoa is almost instantaneous.

Any gene set that doesn't have the correct number of chromosomes almost always stops dividing at the blastocyst stage. It does occasionally happen but it is extremely unlikely.

Check out this article online. It seems suitable for children to read.

Last edited by the_clangers; 17.08.2011 at 03:36.
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  #1218  
Old 17.08.2011, 04:41
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Re: Ask a Scientist

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Anyone get it ?

Attachment 31103
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Eh, ah, your point or question was...............????????????????????????????
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  #1219  
Old 17.08.2011, 07:38
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Re: Ask a Scientist

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The electro chemical reaction that blocks the entrance of an other spermatozoa is almost instantaneous.

Any gene set that doesn't have the correct number of chromosomes almost always stops dividing at the blastocyst stage. It does occasionally happen but it is extremely unlikely.

Check out this article online. It seems suitable for children to read.
Usually, but there are exceptions.

How does someone become a chimera? There are a number of ways this can happen:

Quote:
Q-The other night on CSI they used a medical term (I think it started with a C) for a person that had two different DNA's. Have you ever heard of this?

-A curious adult from Alabama

A-it is possible to become a chimera if developing fraternal twin embryos fuse together to become one embryo. (Think of this is as the reverse of identical twins where a single embryo splits into two.) This happens very early on when the embryos are just unspecialized cells, so a healthy baby can still be made. Fraternal twins do not have the same DNA, so a mixture of two embryos will give a chimera.
http://www.thetech.org/genetics/ask.php?id=23
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  #1220  
Old 17.08.2011, 07:47
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Re: Ask a Scientist

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Why is meltwater from glaciers and snowy peaks distinctively pale blue in colour?
It's the minerals- called rock flour - quartz and feldspar. Beautiful isn't it?

Source:

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