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trutv.com - Stopping a Repo Team is hard to do when you can't leave your yard.
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- olfatsolja, on 10/12/2007, -1/+18or perhaps, obesity in America is changing the gravity fields
- RubeusEsclair, on 10/12/2007, -2/+14Ah... so obesity in America is actually just the gravity fields.....
- cbdgr, on 10/12/2007, -1/+10you mean 9.80665 m·s^2 to be precise
- jofer, on 10/12/2007, -0/+7Believe it or not, it's fairly easy to measure changes in gravity with an absolutely insane degree of precision if you know your elevation and position very accurately (cm scale accuracy). Needless to say, this is a lot harder if you're in orbit or at sea. When you do a microgravity survey on land, you have to correct for nearby cars, trees, buildings, topography, and Earth tides--the effect of tidal forces on solid rock. (A gravimeter is insulated and has in internal thermostat to keep it at a constant temp, so you don't have to worry too much about external temperature) If you're being careful about it, you always stand the exact same way over the gravimeter. It's senseitive enough that whether or not you're wearing a backpack makes a difference. What's even more suprising is that we've been able to measure gravity at this accuracy for a really long time. The LaCoste & Romberg gravity meter is the most common gravimeter used on land--it's basic design hasn't changed since the 1950's. (or sometime around then... I'm not sure exactly when it was invented.) In fact, I'm told the older models are actually more accurate, as the spring used was better quality before they began manfacturing them in larger quantities. (In a modern one, you're basically paying ~2/3 of the cost is for the spring alone... It's a $20,000 spring!) Unfortuately, we can't use that in a satellite.
What's so cool about the GRACE system is that we're able to accurately measure gravity over land from space. It's nowhere near as precise as a microgravity survey, (and couldn't be--too far away from small anomalies, too low a spatial resolution as well.) but land-based gravity surveys require an insane amount of time and planning. We've been able to measure over the sea for quite awhile... It's easy to measure the elevation of the surface of the ocean very accurately over a several sq. km. area. This gives us a rough measurement of the gravity anomaly. (Waves cancel each other out over a large area, and tides, etc can be eaisly corrected for.) Incidentally, this is the way we've been able to map the entire seafloor... (Crude spatial resolution, but good enough for global maps.) Satellites can't see through km's of water, regardless of what's shown in movies. Up until _very_ recently, though, there hasn't been a good way of getting a measurement of the gravity anomaly over land from space. GRACE has changed that.
Now for the (imo, anyway) really neat part. GRACE isn't one satellite, it's two. The way it measures changes in gravity is by very, very, very precisely measureing the distance between the two satellites... Think about it for a second. You've got to know the absolute position (relative to the Earth's surface, anway) in 4 dimensions (3d + time) of the satellites to a cm scale accuracy, and then know the distance between the two satellites, ~200km apart to an accuracy of 10 micrometers! Yes, 10 micrometers accuracy over a 200km distance. All while in orbit around the planet.... How friggin' cool is that?!
Anyway, enough of my geek rant... Obviously, I'm a geophysist, so I happen to think this is neat stuff... At any rate, the data recieved from the satellite makes my work a lot eaiser!
Oh, and on a somwhat related note, the figure in the article isn't showing the shape of the Earth... The Earth isn't a sphere, but it's rounder than your average marble. (And it's changes in shape are far more regular...) What it's showing is changes in gravity. These have been corrected for topography, and are mostly due to density variations in the crust and mantle, as the article states... - ahawks, on 10/12/2007, -0/+7I don't see it on planets.com, but even if it is there... I am sure it would be to eliminate things like asteroids and Borg cubes from qualifying as planets.
- ahawks, on 10/12/2007, -1/+8ummmm, proportionally, the earth is smoother and more spherical than a pool ball.
Besides, all planets, and all stars, are slightly elliptical because of their rotation.
Also, where did you get this idea that the definition of a planet includes "round"? - Klowner, on 10/12/2007, -0/+7it's pulling on your no-no bits, isn't it?
- Klowner, on 10/12/2007, -0/+7That explains why all those photographs I've seen of Sri Lanka have helium balloons tied to everything
- oslointhesummer, on 10/12/2007, -0/+6I want to know the maximum difference, between the highest and lowest gravities on earth. The article doesn't give any specific figures.
- Jugalator, on 10/12/2007, -0/+6"you mean 9.80665 m·s^2 to be precise"
Yes, as for the definition. However, in the real world varying from 9.78 - 9.83.
(just in case someone believed that value is constant in the world) - elastikos, on 10/12/2007, -0/+5Sorry I should have looked at http://en.wikipedia.org/wiki/Gravity before posting that figure. I was using my unreliable grey amygdala for referencing grade 11 physics!
9.81 m/s² or 32.2 ft/s² - ChileanGoD, on 10/12/2007, -0/+4Let him alone guys... he was smoking marijuana.. that's why the world seamed to have a 9.2m/s¨2 gravitational pull.
- kodeiko, on 10/12/2007, -1/+5Err isn't it 9.8?
- webcrumb, on 10/12/2007, -0/+3"Meters? Speak American, boy!"
You've already translated metres into American... - elastikos, on 10/12/2007, -2/+5That is some advanced imagery and science. 9.2m/s is not right everywhere around the world then!
- ChileanGoD, on 10/12/2007, -1/+4You can even see the little red dot where Michael Moore is standing.
- AngryPenguin47, on 10/12/2007, -0/+3He is a collapsed neutron star, he has his own intense gravitational field.
- czer323, on 10/12/2007, -1/+4It's not a tumah!
- oogee, on 10/12/2007, -0/+2most of the time, but not all of the time.
- DiamondIce, on 10/12/2007, -0/+2That's a proposal. It won't be taken into vote until the 24th, and even then it's not clear if it will pass. Until the 24th (and possibly after) the word "planet" doesn't really have a definition, and therefore doesn't contain the word "round."
- affanjam, on 10/12/2007, -1/+3http://space.com/scienceastronomy/060816_planet_definition.html
- ChileanGoD, on 10/12/2007, -0/+1You gus have to be pulling everything to your country hug? Oil.. Money... Now this. :)
- olddirtycr, on 10/12/2007, -3/+3oh no earth has a tumor!
- ahawks, on 10/12/2007, -3/+2Just to demonstrate further,
http://dictionary.reference.com/browse/planet
1. A nonluminous celestial body larger than an asteroid or comet, illuminated by light from a star, such as the sun, around which it revolves. In the solar system there are nine known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
2. One of the seven celestial bodies, Mercury, Venus, the moon, the sun, Mars, Jupiter, and Saturn, visible to the naked eye and thought by ancient astronomers to revolve in the heavens about a fixed Earth and among fixed stars.
3. One of the seven revolving astrological celestial bodies that in conjunction with the stars are believed to influence human affairs and personalities. - bobotheking, on 10/12/2007, -2/+1Gravity's rainbow? Insert witty, Pynchon-esque comment here...
- olddirtycr, on 10/12/2007, -4/+2planets.com says all planets must be round
- inactive, on 10/12/2007, -8/+6Meters? Speak American, boy! 32.2 f/s^2
< / sarcasm >
@kodeiko
It might be 9.2 in Sri Lanka :-P - oogee, on 10/12/2007, -5/+1Is gravity gay?
- affanjam, on 10/12/2007, -11/+5Earth is not round anymore, so doesn't that mean earth is not a planet anymore?
