Why are snowflake crystals symmetrical? Most crystaline snowflakes are six sided. Why do all six rays of the snowflake crystal match? A snowflake crystal can be quite elaborate, and yet all six rays are just about exactly the same. Why isn't every other ray different? Or why aren't all six rays unique from each other?

The six sides of a snowflake are very similar, but they're not the same. They're similar because they all formed in very similar conditions. There is some randomness to it, which helps prevent snowflakes from being perfectly symmetric, but by and large crystal growth patterns for a given substance are dictated by the conditions under which they formed.

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I don't know, I've been looking at some of the snowflakes photographed by Wilson Bentley and they look pretty symmetrical to me. Do you have a link to some information Kristophe?

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Here's a pretty good explanation with diagrams:
http://deepimpact.jpl.nasa.gov/educ/IceCream04.html

I've been looking at some of the snowflakes photographed by Wilson Bentley and they look pretty symmetrical to me.

Yeah, but these are professional studio snowflakes. Like all models, they are selected for their, um, physical perfection. (It's rumoured some even undergo reconstructive surgery, though they will deny it!!)

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I can do better than that. kucharek's link has pictures of snowflakes that aren't perfectly symmetrical. Keep in mind that I'm not arguing that snowflakes aren't nearly perfectly symmetrical (a good 40 minutes of searching Google shows that most science orientated websites and/or ezines use the phrases "nearly perfect" or "nearly symmetrical" a lot).

This snowflake shows several blemishes. If you check the edges of the points, you'll notice that they're not exactly the same. The top central point has a slight indentation just to the left of its peak. The top right point has a groove running along its upper flank that isn't found on the other points. The bottom left point shows an indentation similar to that seen in the top central, only in a different position. The "fins" found closer to the base of each of the points are far less than perfect.

The closer you look, the less perfect the snowflakes will look.

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comedy gold.
taks

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Nice website with good explanations of the growth. The short answer is that the six-fold symmetry reflects the underlying symmetry of the water crystal structure.

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Interesting article Blob. It also reminded me of a lot of MIAs, like Kucharek and Taks.

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I had to read most of the article to figure out when they were talking about crystals and when they were talking about aggregations.

They use the word "flake" way to often which makes the article...well, Flaky. I'd like it if it were more Crystal clear.

Anyway, Frisbee size kind of suprises me, but around here, when the snow is "sticky" and warmer (relative term of course), the aggregates get quite large. I've seen golfball sized quite often, and almost baseball size on very rare instances.

My big question. How do you measure the size of a snowflake from a satellite or a plane?
Ok; with lasers, but how?

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Must take a lot of patience to photograph them. You must have to work outdoors, and you can't touch them at all right?

What do you do, just set a bunch of slides outside during a snowfall, then wait nearby with microscope?

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From what I understand about microphotography of snowflakes - yes, that is exactly it.

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For many years my dad was on the ski patrol and worked in avalanche control. At one point in this career, he was the instructor in a weekend class he refers to as "Snow Physics". It was basically a how and why hazardous conditions build up and how they can be spotted early. One of the things he mentioned to me once was that as the temperature drops, the flakes get smaller. The reasons for this were never explained, but I'd have to say it's because the snow is still a bit wet and it sticks together better. My observations have been that when it's warmer, the flakes come down in masses rather than individuals.

I also asked him if it was possible for it to get too cold to snow. He said it was, but it wasn't likely to happen outside of the poles, because the cold will draw all the water out of the clouds on the outer edges of the really cold zone.

I'd actually like some verification on that if anyone knows for sure. Not that I don't trust him, but I'm not quite ready to list him as a source on this.

About photographing flakes: I gave it a shot a few weeks ago. We had a few really cold nights and when that happens, there will be snowflakes that can be easily seen as individuals against a dark background, such as my car. I have a 300mm lens with a macro setting so I was able to find a spot where there were just three in the frame. Then technology struck.
As it turns out, the focal plane of the film and the viewfinder are about 0.75 mm different. (I leaned this by messing up a picture of a jumping spider). Also the camera used the dark background of the car for the exposure settings rather than the flake in the center, so I ended up with a blurry, over exposed white blob, that may well be a streetlight if you didn't know better. I waited three years to catch those conditions too.

BTW, it didn't actually snow that night. It just cold and very humid.

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And when the water is out of the cloud, what's left?
Well, I don't know for sure, my limit is a meteorology class in college. I just felt I needed to chime in on the above statement. But; my understanding is that the colder it gets, the air can't hold enough moisture to for the condensation to occur.

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Nothing. The clouds dissipate which is why there seems to be so many cloudless days in pictures from the poles.

Maybe that's it. Anyway, that was why I asked for a second opinion on it.

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A Nerd can figure out how long it will take the original Enterprise traveling at warp 6.5 to travel from Regulus to Antares.
A Geek will think he can use that to pick up a girl in a bar.
A Dork knows he can't pick up the girl with it, but will hang around for hours anyway, just in case she asks.
She might. You never know.

My recollection too, from the same classes probably. As a Geography student, I took a few classes in climatology and meteorology (which I sometimes have to tell people is not about meteors).

But yeah, the colder the air mass, the less moisture it can hold. Think absolute versus relative humidity. Most weather reports give relative humidity, expressed as a percentage. Absolute humidity is expressed as the amount of moisture in a given volume of air. I can't even remember the units usually used.

Cold air can have enough moisture to measure as a decent relative humidity level, but the absolute volume of moisture in the air might be very low. Conversely, there is that "dry" heat Arizonans brag about. In that situation the moisture content (absolute) is deceptively high, but the capacity of the air mass (to hold water) is so high that the relative humidity is very low.

Apologies for all the vague adjectives; the absolutes are long forgotten. I would just add that relative humidity is what is used most often simply because it is easier for humans to guage their expected comfort level using that measure.

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