Starship Asterisk*

If Saturn's South Pole wasn't strange enough with its rotating vortex,

flabbergasted man wrote:Let's ask the bees, why a hexagon is so stable. c

lakeside wrote:I like my crackpot theory that the hexagon is the cloud top manifestation of the largest ice crystal reef in the solar system.

JW

walfy wrote:I'm surprised the APOD writers didn't even know that very excellent science was done in trying to figure out this strange structure. Here's your answer: http://www.planetary.org/blogs/emily-la ... /2471.html

delgado wrote:I have seen this beautiful image of the Saturn hexagon. In the explanation it is said that the jovian plane eclipses the Saturn rings. I think his a mistake: jovian planet is Jupiter, isn't it? Can 'jovian' be used also for Saturn? Thanks

A gas giant (sometimes also known as a jovian planet after the planet Jupiter, or giant planet) is a large planet that is not primarily composed of rock or other solid matter.

walfy wrote:I'm surprised the APOD writers didn't even know that very excellent science was done in trying to figure out this strange structure. Here's your answer: http://www.planetary.org/blogs/emily-la ... /2471.html

Creating Saturn's hexagon in the laboratory

This is a top-down view of a laboratory tank in an experiment designed to reproduce the wind conditions near Saturn's north pole. The whole cylindrical tank is 60 centimeters wide. Its lid and base are split into two concentric sections, with the inner circle being 30 centimeters in diameter. The inner and outer circles are rotated at different rates, which sets up an instability at their boundary, producing a standing wave; the number of waves it takes to encircle the "pole" depends on various experimental parameters, including the rotation speed. In this particular case, the wavenumber is 6, producing a hexagon. Dye has been injected into the tank to make the form of the turbulent flow visible. Eddies are produced outside the wave.

rstevenson wrote:It seems complex systems, given the right conditions, naturally create geometric shapes, if not always stable ones.

Indigo_Sunrise wrote:Very intriguing image!
One question: why does the link in this sentence (from the description; emphasis added):

If Saturn's South Pole wasn't strange enough with its rotating vortex,

take the user to an APOD that features Saturn's North Pole? Or is the link just an extremely close up view of the hexagon?

Chris Peterson wrote:

rstevenson wrote:
Just a few days ago I watched a recent episode of PBS's excellent Nova program, Earth From Space. Part way through it, in a section about weather systems around Antarctica, they showed a time-lapse video of low-pressure systems whirling around the continent over the space of months. A sometimes hexagonal pattern appeared in a kind of pulsating way, not always there, not always hexagonal, but definitely a pattern. It seems complex systems, given the right conditions, naturally create geometric shapes, if not always stable ones.

It is worth noting that outside of carefully contrived setups, no complex system (which, in fact, includes systems that might seem incredibly simple to us) are stable. It's always a question of how long some sort of metastability can be maintained.

http://en.wikipedia.org/wiki/Rossby_Waves wrote:

[img3="Meanders of the northern hemisphere's jet stream developing (a, b) and finally detaching a "drop" of cold air (c). Orange: warmer masses of air; white: jet stream. [If the Earth rotated in just
10.6 hours the polygonal pattern would be MUCH more stable]"]http://upload.wikimedia.org/wikipedia/c ... aves_N.gif[/img3]

<<Atmospheric Rossby waves are giant meanders in high-altitude winds that are a major influence on weather.

Atmospheric Rossby waves emerge due to shear in rotating fluids, so that the Coriolis force changes along the sheared coordinate. In planetary atmospheres, they are due to the variation in the Coriolis effect with latitude. The waves were first identified in the Earth's atmosphere in 1939 by Carl-Gustaf Arvid Rossby who went on to explain their motion.

One can identify a Rossby wave in that its phase velocity (that of the wave crests) always has a westward component. However, the wave's group velocity (associated with the energy flux) can be in any direction. In general, shorter waves have an eastward group velocity and long waves a westward group velocity.

The terms "barotropic" and "baroclinic" Rossby waves are used to distinguish their vertical structure:

• 1) Barotropic Rossby waves do not vary in the vertical, and have the fastest propagation speeds.
  2) The baroclinic wave modes are slower, with speeds of only a few centimetres per second or less.

Most work on Rossby waves has been done on those in Earth's atmosphere. Rossby waves in the Earth's atmosphere are easy to observe as (usually 4-6) large-scale meanders of the jet stream. When these deviations become very pronounced, they detach the masses of cold, or warm, air that become cyclones and anticyclones and are responsible for day-to-day weather patterns at mid-latitudes. Rossby waves may be partly responsible for the fact that eastern continental edges, such as the Northeast United States and Eastern Canada, are colder than Europe at the same latitudes.>>

http://en.wikipedia.org/wiki/Hex_sign wrote:

[b][color=#0000FF]Saturn's north pole vortex, as viewed at 750 nm through a polarizer[/color][/b]

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<<Hex signs are a form of Pennsylvania Dutch folk art, related to fraktur, found in the Fancy Dutch tradition in Pennsylvania Dutch Country. Barn paintings, usually in the form of "octagon or hexagon stars in circles," grew out of the fraktur and folk art traditions about 1850 when barns first started to be painted in the area. Prior to the 1830s, the cost of paint meant that most barns were unpainted. The geometric patterns of quilts can be seen in the patterns of many hex signs.

The term hex with occult connotations may derive from the Pennsylvanian German word "hex" (German "Hexe", Dutch "Heks"), meaning "witch." However the term "hex sign" was not used until the 20th Century, after 1924 when Wallace Nutting's book Pennsylvania Beautiful was published. Before this time many Pennsylvania German farmers simply called the signs "blumme" or "schtanne" (meaning flowers or stars). However one farmer used the term "Hexefoos" in his description.

Some view the designs as decorative symbols of ethnic identification, possibly originating in reaction to 19th century attempts made by the government to suppress the Pennsylvania German language. Anabaptist sects (like the Amish and Mennonites) in the region have a negative view of hex signs. It is not surprising that hex signs are rarely, and perhaps never, seen on an Amish or Mennonite household or farm.>>

MargaritaMc wrote:

delgado wrote:I have seen this beautiful image of the Saturn hexagon. In the explanation it is said that the jovian plane eclipses the Saturn rings. I think his a mistake: jovian planet is Jupiter, isn't it? Can 'jovian' be used also for Saturn? Thanks

The quick answer is, "Yes."

http://en.m.wikipedia.org/wiki/Gas_giant

A gas giant (sometimes also known as a jovian planet after the planet Jupiter, or giant planet) is a large planet that is not primarily composed of rock or other solid matter.

Margarita

walfy wrote:I'm surprised the APOD writers didn't even know that very excellent science was done in trying to figure out this strange structure. Here's your answer: http://www.planetary.org/blogs/emily-la ... /2471.html

delgado wrote:I have seen this beautiful image of the Saturn hexagon. In the explanation it is said that the jovian plane eclipses the Saturn rings. I think his a mistake: jovian planet is Jupiter, isn't it? Can 'jovian' be used also for Saturn? Thanks

delgado wrote:In this case, jovian should not be with capital, "Jovian", as it is, but rather as "jovian" , since it is not a proper name but an adjectiv.

Chris Peterson wrote:

delgado wrote:
In this case, jovian should not be with capital, "Jovian", as it is, but rather as "jovian" , since it is not a proper name but an adjectiv.

In English, it is usual, although not universal, to retain the capital for adjectives derived from proper nouns. The several dictionaries I checked all list "Jovian" only as a capitalized adjective. That said, however, I think this is largely about style, and not any absolute rules. I'd consider either usage equally acceptable. In my own usage, I'd probably be inclined to use "jovian" in reference to the class of jovian planets, and "Jovian" when referring to Jovian winds [on Jupiter].