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Old 08-14-08, 07:26 PM   #1
Allen
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Real Question--Astronomy

I was reading about the hexagon circling Saturn's north pole (which may be the oddest weather feature on any planet in the solar system) and it came to me that I have no idea how wind speed is determined on a gaseous planet. On the Earth, wind speed is measured relative to the solid ground. What is the relative marker used on a planet that has no solid surface?

For that matter how is the rotational period for the gas giants determined, given that the upper atmosphere (which is the part visible to us) may outpace, or even travel in the opposite direction of the core of the planet?
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Old 08-14-08, 07:52 PM   #2
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I was reading about the hexagon circling Saturn's north pole (which may be the oddest weather feature on any planet in the solar system) and it came to me that I have no idea how wind speed is determined on a gaseous planet. On the Earth, wind speed is measured relative to the solid ground. What is the relative marker used on a planet that has no solid surface?

For that matter how is the rotational period for the gas giants determined, given that the upper atmosphere (which is the part visible to us) may outpace, or even travel in the opposite direction of the core of the planet?
When a planet rotates, it wobbles slightly, especially if it has moons. The wobble is very detectable and that's how they measure the rotational period. Knowing that, they can figure the delta between moving gases and the planets overall rotation.

The density of the planet would have to be absolutely and perfectly uniform for it not to wobble. (see? I didn't split my infinitive)
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Old 08-14-08, 07:56 PM   #3
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Thanks. That makes sense.




Southerners have a genetic deficiency in grammar.
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Old 08-14-08, 08:01 PM   #4
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I was reading about the hexagon circling Saturn's north pole (which may be the oddest weather feature on any planet in the solar system)
Wow, that's nuts.
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Old 08-14-08, 08:09 PM   #5
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The South pole has a giant reverse tornado like storm. Instead of flowing from the base of the funnel up, it goes the other way.

Cool too, but the hexagon is just weird.
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Old 08-14-08, 08:26 PM   #6
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Southerners have a genetic deficiency in grammar.
It was a cross-thread inside joke...

I spent 10 years in Atlanta... luckily I found enough other yankees at school to keep me feeling at home...
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Old 08-14-08, 08:39 PM   #7
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Musta have gone to Emory.
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Old 08-15-08, 01:06 AM   #8
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When a planet rotates, it wobbles slightly, especially if it has moons.
The problem is in a gaseous planet, that wobble represents a lot of "sloshing" mass rather than an absolute period.

In Saturn's case, there's several different accounts of the length of a day that vary by about 10 minutes. Some are based on the rotation of the cloud bands, which due to viscosity move approximately at the speed of the bulk of the planet. One that was thought to be pretty solid was a periodic radio wave that emanates from Saturn, but this too was found to vary, as it appears to be caused by the movement of a layer of plasma inside Saturn.

Still, that margin of error is only about 2-3%

http://en.wikipedia.org/wiki/Saturn#Orbit_and_rotation
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Old 08-15-08, 04:22 AM   #9
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Musta have gone to Emory.
Georgia Tech
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Old 08-15-08, 05:25 AM   #10
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The hexagon shape's been replicated on earth in spinning fluids before. They've gotten a lot of weird shapes in it.
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Old 08-15-08, 06:45 AM   #11
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Georgia Tech
So you sell fries for a living then. Got it.
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Old 08-15-08, 07:12 AM   #12
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So you sell fries for a living then. Got it.
Please... *sigh*
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Old 08-15-08, 07:15 AM   #13
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Please... *sigh*
oh...you graduated up to the burger flipper?
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Old 08-15-08, 07:25 AM   #14
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oh...you graduated up to the burger flipper?
Don't you understand that stereotype jokes are funny if and only if there is at least some sliver of truth to them?

Trying to use the burger-flipper joke against a Tech grad is like trying to use poverty jokes against Donald Trump. It just doesn't work.

Hope this helps.
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Old 08-15-08, 07:28 AM   #15
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Don't you understand that stereotype jokes are funny if and only if there is at least some sliver of truth to them?

Trying to use the burger-flipper joke against a Tech grad is like trying to use poverty jokes against Donald Trump. It just doesn't work.

Hope this helps.
Not a bit...you do understand this is foo.....right? We do very little in a serious manner in here. And for what its worth, I have known several tech grads who flipped burgers for a living. It helped that they owned the franchise, so they were just contributing to their own bottom line, but it fit the stereotype perfectly.

Hope this helps.
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Old 08-15-08, 07:34 AM   #16
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Not a bit...you do understand this is foo.....right? We do very little in a serious manner in here. And for what its worth, I have known several tech grads who flipped burgers for a living. It helped that they owned the franchise, so they were just contributing to their own bottom line, but it fit the stereotype perfectly.

Hope this helps.
If they owned the franchise, they were not flipping burgers "for a living." That was not their primary job function. Their primary job function was to act in the capacity as the owner of the business. If it made economic sense for them to assume the duties of a rank and file employee, then that was the decision they made that was in the best interest of their concern.

The burger-flipping joke is intended to imply a personal lack of intelligence, wealth, or usefulness. It is not meant to be a compliment to someone's success.

So, it doesn't stand to reason that "it fit the stereotype perfectly."

btw: "Don't take the ribbing personally." Adverbs are your friend. It is awkward to modify verbs with adjectives.
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Old 08-15-08, 07:40 AM   #17
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Sheesh...are you serious? You come in to foo, a place known not to be the most serious place on the web, and take offense at a stereotype joke about a F'ing school?! WTH is up with that. And then on top of that, you quote a PM (P is for PRIVATE) in your post and try to be an Fing grammar nazi about that as well?
Congrats, you are the first fooster I will ignore, and I've been here for a while.
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Old 08-15-08, 08:15 AM   #18
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Sheesh...are you serious? You come in to foo, a place known not to be the most serious place on the web, and take offense at a stereotype joke about a F'ing school?! WTH is up with that. And then on top of that, you quote a PM (P is for PRIVATE) in your post and try to be an Fing grammar nazi about that as well?
Congrats, you are the first fooster I will ignore, and I've been here for a while.
I never took offense to any of it and I still don't. I was simply pointing out the problems in your logic.

The joke would have been funny had you said something like "So, I guess your computer is your girlfriend," or, "Win any football games lately? (sarcastically)" That's the kind of stuff Tech people are known for, and those would have been really funny, and I might have even laughed.

I don't mind people making jokes about Tech and Tech people, but they should be at least appropriate, relevant, and funny.

I'm just trying to help.
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Old 08-15-08, 09:21 AM   #19
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My guess is that the hexagonal feature is formed by one central (polar) vortex surrounded by six similar vortices, equally spaced. Perhaps they're subpolar and that the circumference at that latitude holds six stable vortices. Fewer, and they become unstable and break up, forming more. More than six, and the excess vortices are ejected to lower latitudes or merged with neighbouring ones. With six stable vortices, the edges will appear somewhat straight, and would also be stable for decades, provided the vortices are large enough.

Just my off-the-top-of-my-head theory.
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Old 08-15-08, 01:38 PM   #20
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Well, remember, a line on the surface of a sphere that appears straight in in fact not straight at all. So it's perfectly reasonable to postulate that some kind of rotational force is creating them.
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