The True Shape of Snowflakes
April 10, 2013 1:01 PM Subscribe
Snowflakes in freefall "The classic image of a snowflake is a fluke. That flat, six-sided crystal with delicate filigree patterns of sharp branches occurs in only about one in every 1000 flakes. And a snowflake seen in 3D is another beast entirely"
BeeDo, off the top of my head, I would guess it has to do with the type of crystal that water forms when its molecules join without too many other forces interfering. Some things have 3-D crystals, but others maybe are biased towards lateral spreading because of the pattern the molecules are organized into.
posted by BlackLeotardFront at 1:13 PM on April 10, 2013
posted by BlackLeotardFront at 1:13 PM on April 10, 2013
Is this some way of trying to keep me from repressing the fact that the Twin Cities is due for 6-10" of snow in the next couple of days?
posted by sparklemotion at 1:15 PM on April 10, 2013
posted by sparklemotion at 1:15 PM on April 10, 2013
One of those pictures in the second link definitely ain't a snowflake.
posted by EmpressCallipygos at 1:19 PM on April 10, 2013
posted by EmpressCallipygos at 1:19 PM on April 10, 2013
Maybe somebody dropped it off a nearby ski lift?
posted by Greg_Ace at 1:34 PM on April 10, 2013 [2 favorites]
posted by Greg_Ace at 1:34 PM on April 10, 2013 [2 favorites]
BeeDo: Thank you. That falls squarely into "things I forgot I always wondered": why are snowflakes flat?Actually, the water crystals encourage flat spread at the atomic level. Hexagons like to lie alongside hexagons - think of sheets of honeycombs, which tend to have a very layered appearance (2d structure, one on top of another). If nothing disturbs the crystal growth, you'd expect a fairly flat crystal... but as the lede notes above, that's fairly rare outside of lab conditions.
posted by IAmBroom at 1:43 PM on April 10, 2013
Maybe somebody dropped it off a nearby ski lift?
Ahh.. the penny drops.
posted by panaceanot at 6:18 PM on April 10, 2013 [2 favorites]
Ahh.. the penny drops.
posted by panaceanot at 6:18 PM on April 10, 2013 [2 favorites]
I had four inches of the crap on my car this morning... I don't care what it looks like anymore.
posted by Mojojojo at 8:59 PM on April 10, 2013
posted by Mojojojo at 8:59 PM on April 10, 2013
Flat snowflakes are flat because of the temperature at which they form. All ice crystals tend to form hexagonal prism shapes, but whether they form a flat hexagonal plate or a long hexagonal needle shape depends on the ambient temperature during growth. Sometimes a snowflake will start out at a temperature that favors needle growth and then drift into another area whose temperature favors plate growth, resulting in a capped column (image is from halfway down this page, which has an excellent taxonomy of different snowflake shapes.) Here's a chart showing how shape varies with temperature. (I have done a great deal of digging around in the literature to see if anyone has a definitive explanation why ice growth shows this temperature dependence, but I haven't found much.)
The feathery multi-branched structure of the classic snowflake (which is officially called a "stellar dendrite") happens due to something called the branching instability. The points of a six-sided hexagonal plate poke out a little further than the sides, and are therefore exposed to slightly more vapor, so they grow slightly faster. Now they stick out even more, so they grow even faster, and begin to develop into a spike. The sub-branching and other details result from the complicated history of the snowflake as it tumbles through my butt from micro-environment to micro-environment. The reason you can get that marvelous combination of symmetry and complexity in a snowflake is because the growth is almost completely controlled by temperature and humidity, so all of its six arms experience exactly the same series of changes and end up exactly the same shape. In the ideal case, of course.
The snowflakes in the article are mostly stellar dendrites, but it looks like there are some clusters of needles and there are some capped columns and bullet rosettes near the end. It's a shame the heavy layers of rime tend to obscure their shape; I'd like to see this same technique used under different weather conditions where you get more well-defined crystals. Very, very cool nonetheless.
posted by fermion at 2:16 AM on April 11, 2013 [3 favorites]
The feathery multi-branched structure of the classic snowflake (which is officially called a "stellar dendrite") happens due to something called the branching instability. The points of a six-sided hexagonal plate poke out a little further than the sides, and are therefore exposed to slightly more vapor, so they grow slightly faster. Now they stick out even more, so they grow even faster, and begin to develop into a spike. The sub-branching and other details result from the complicated history of the snowflake as it tumbles through my butt from micro-environment to micro-environment. The reason you can get that marvelous combination of symmetry and complexity in a snowflake is because the growth is almost completely controlled by temperature and humidity, so all of its six arms experience exactly the same series of changes and end up exactly the same shape. In the ideal case, of course.
The snowflakes in the article are mostly stellar dendrites, but it looks like there are some clusters of needles and there are some capped columns and bullet rosettes near the end. It's a shame the heavy layers of rime tend to obscure their shape; I'd like to see this same technique used under different weather conditions where you get more well-defined crystals. Very, very cool nonetheless.
posted by fermion at 2:16 AM on April 11, 2013 [3 favorites]
I would like to present to fermion the 2013 award for best use of a browser extension in an educational metafilter post. Edutainment at its best!
Second line of the second paragraph.
posted by Spiegel at 7:30 AM on April 11, 2013 [2 favorites]
Second line of the second paragraph.
posted by Spiegel at 7:30 AM on April 11, 2013 [2 favorites]
Oh man, I didn't realize it did that to text entry boxes too. Thanks, Cloud to Butt Firefox Extension.
posted by fermion at 9:05 AM on April 11, 2013
posted by fermion at 9:05 AM on April 11, 2013
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posted by BeeDo at 1:09 PM on April 10, 2013