Researchers Develop the Most Detailed Map of Gravitational Variations Ever

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Researchers Develop the Most Detailed Map of Gravitational Variations Ever

Posted by samzenpus on Monday September 16, 2013 @01:41AM from the he's-not-heavy dept.

schliz writes "An Australian-German team of researchers has developed the most detailed map of gravitational variations ever, using satellite data, gravitational readings and small-scale topographical models. They say the data will help civil engineers and miners, and will be available for free online. Gravitational fields vary because the Earth isn't perfectly spherical. According to the new map, the field is 0.7% greater near the North Pole (9.83ms-2) than at Peru's Nevado Huascaran summit (9.76ms-2). The difference is 40% more than previously expected."

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direct link by schneidafunk · 2013-09-16 01:45 · Score: 5, Informative

Here is a direct link to the map if you are wondering where you'll be the lightest :)

--
Some people die at 25 and aren't buried until 75. -Benjamin Franklin
1. Re:direct link by Anonymous Coward · 2013-09-16 01:58 · Score: 0, Offtopic
  
  In related news, the Parkinson's Spirograph Project has announced that they have misplaced this year's submissions. They have officially declared it a tie.
2. Re:direct link by Cryacin · 2013-09-16 02:17 · Score: 4, Funny
  
  The important question: Are they attracting tenure with the weight of their research?
  
  --
  Science advances one funeral at a time- Max Planck
3. Re:direct link by LWATCDR · 2013-09-16 02:29 · Score: 2
  
  Probably should be most detailed map released to the public. The Military of both the US and Russia/USSR have been working on maps of gravitational variations for decades.
  
  --
  See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.
4. Re:direct link by Anonymous Coward · 2013-09-16 02:40 · Score: 1
  
  Civilian uses for high resolution maps include mineral prospecting.
5. Re:direct link by dotancohen · 2013-09-16 02:56 · Score: 1
  
  Here is a direct link to the map if you are wondering where you'll be the lightest :)
  Where is the lowest spot?
  http://physics.stackexchange.com/questions/22613/lowest-gravity-on-earths-surface
  
  --
  It is dangerous to be right when the government is wrong.
6. Re:direct link by rwise2112 · 2013-09-16 02:59 · Score: 2
  
  Probably should be most detailed map released to the public. The Military of both the US and Russia/USSR have been working on maps of gravitational variations for decades.
  It would also be only the most detailed measured using sattelites. More detailed maps can be made using measurements from airborne gravimeters or surface measurements. They are used often for oil and mineral exploration.
  
  --
  
  "For every expert, there is an equal and opposite expert"
7. Re:direct link by Anonymous Coward · 2013-09-16 03:57 · Score: 0
  
  Where's my mod points when I need them?
8. Re:direct link by edumacator · 2013-09-16 06:38 · Score: 1
  
  Hey. Don't make light of the gravity of this research.
  
  --
  An important change for education.
9. Re:direct link by scuzzlebutt · 2013-09-16 07:49 · Score: 1
  
  If all the obese people go there, wouldn't that at least begin to mitigate the gravity variance?
  
  --
  In C++, your friends can see your privates.
10. Re:direct link by Platinumrat · 2013-09-16 09:21 · Score: 1
  
  Interesting you say that. The way grant funding works in Australia is different from the US. In Australia you can get grant funding becasue you've previously done good research before. Thus, the funding is along the lines of... "You've done good work, so we'll keep funding you to continue researching".
11. Re:direct link by ArsonSmith · 2013-09-16 09:51 · Score: 1
  
  It's nice to hear that another country has found a fair and balanced way to quantify "good work." because here in the US it's all about what you can convince someone as "good work" leading to requiring far more political/sales/marketing skills and the research itself is secondary to that.
  So what is the fair and balanced weighting of "good work" to which you employee?
  
  --
  Paying taxes to buy civilization is like paying a hooker to buy love.
Your Mom's House by Esion+Modnar · 2013-09-16 01:45 · Score: 4, Funny

The gravity field spikes hard there.

--

They say the first thing to go is your penis. Well, it's either that or your brain. I forget which...
1. Re:Your Mom's House by Anonymous Coward · 2013-09-16 02:02 · Score: 0
  
  Her house? You can make out each of her thighs.
2. Re:Your Mom's House by Anonymous Coward · 2013-09-16 02:03 · Score: 0
  
  Must be because of my gigantic penis. She just kinda gravitated toward it.
3. Re: Your Mom's House by peragrin · 2013-09-16 02:09 · Score: 1, Informative
  
  Actually the opposite is true. The more mass you have between the gravity source and your self the lower the gravitational pull is.
  Though why Everest has higher gravity than a mountain in Peru is odd. Unless the lost city of gold is under that mountain.
  The bigger the object the greater the gravitational field. However the more mass you have between yourself and said field point"source" the lower the effects of gravity you feel.
  
  --
  i thought once I was found, but it was only a dream.
4. Re: Your Mom's House by Anonymous Coward · 2013-09-16 02:13 · Score: 0
  
  Sounds like someone has a fat mom.
5. Re: Your Mom's House by somersault · 2013-09-16 02:30 · Score: 1
  
  The more mass you have between the gravity source and your self the lower the gravitational pull is
  That doesn't make any sense to me.. mass is your "gravity source". Though due to the inverse square nature of gravitational pull, putting yourself on top of a mountain would probably reduce the overall gravitational force exerted on your body much more than it adds to it (owing to you getting further from the centre of the Earth). Especially if the mountain was tall, thin, and had a low density.
  
  --
  which is totally what she said
6. Re: Your Mom's House by Skapare · 2013-09-16 02:33 · Score: 1
  
  Being on top of a higher mountain places you further from the all that mass of the whole planet, reducing your gravity. How it is that they are showing higher gravity for some mountains is not understood.
  
  --
  now we need to go OSS in diesel cars
7. Re: Your Mom's House by Anonymous Coward · 2013-09-16 02:39 · Score: 0
  
  Uh, no, that's not how it works at all. Mountains are massive.
8. Re: Your Mom's House by camperdave · 2013-09-16 02:52 · Score: 3, Interesting
  
  True, but the real question is whether the increase in gravitational pull due to the extra mass of the mountain is greater than or less than the decrease in gravitational pull you experience by being further away from the center of the Earth due to the height of the mountain.
  
  --
  When our name is on the back of your car, we're behind you all the way!
9. Re: Your Mom's House by HybridST · 2013-09-16 03:25 · Score: 1
  
  Look up Newtons Theorem and try again.
  
  --
  Ever notice that Cobra Commander sounds an awful lot like Star scream?
10. Re:Your Mom's House by wbr1 · 2013-09-16 03:45 · Score: 1
  
  Screw you man, screw you!
  I am not mad about your joke at my mothers expense, just that I was going to make the same joke about my ex-wife!
  
  --
  Silence is a state of mime.
11. Re: Your Mom's House by lymond01 · 2013-09-16 04:06 · Score: 1
  
  Agreed. From the map they're obviously not just measuring altitude and running it through Newton's equation with R being the distance to the center of the Earth. Or maybe they are if the world isn't perfectly elliptical (as noted in the article). If the Peruvian mountains are tall but overall set in a portion of Earth closer to the center of mass, then their gravity at the peak might be stronger than other equally high mountains. Or maybe they are taking into account on site measurements as well. A satellite can't really tell how close to the Earth's center of mass it is, can it? I suppose I should just read their methodology.
  And I'm still hoping for an anti-gravity cloak. Or perhaps a good explanation of gravitons or what is warping spacetime.
12. Re: Your Mom's House by peragrin · 2013-09-16 04:46 · Score: 1
  
  The survey shows that is wrong. Everest has greater gravity acceleration than a mountain 7,000 ' shorter.
  
  --
  i thought once I was found, but it was only a dream.
13. Re: Your Mom's House by Anonymous Coward · 2013-09-16 04:58 · Score: 2, Interesting
  
  If you RTFA...
  
  All quantities are given at the Earth’s surface as defined through the SRTM (Shuttle Radar
  421 Topography Mission) topography. Users wishing to use geoid heights instead of quasigeoid
  422 heights can do so by applying standard conversion as described, e.g., Rapp [1997].
  If you want a more generic explanation of gravity anomalies? Perhaps this will help... http://www.cage.curtin.edu.au/~will/grav_anoms.htm
14. Re: Your Mom's House by K.+S.+Kyosuke · 2013-09-16 05:05 · Score: 1
  
  the extra mass of the mountain...
  ...is at least partly compensated for. It's not just "some extra stuff on top of something that exactly the same as places without extra stuff on top": the mountains float on the denser mantle with the rest of the Earth's crust, with a greater portion of the lighter crust material reaching deeper into the mantle, creating a "negative mascon" under the "extra mountain". It's somewhat like ice on sea - there's light stuff under the surface, too.
  
  --
  Ezekiel 23:20
15. Re: Your Mom's House by OldSoldier · 2013-09-16 05:32 · Score: 1
  
  They say it's a "gravitational map" but is it with or without the effects of the earth's rotation? How much less do you weigh because the earth's rotation is trying to fling you off it on a mountain top (longer radius arm) near the equator (faster rotational speed)?
16. Re: Your Mom's House by Anonymous Coward · 2013-09-16 07:12 · Score: 0
  
  It's accounted for. http://en.wikipedia.org/wiki/Physical_geodesy. Next up, let's debate quantum mechanics on Slashdot... first post should be on whether we should call the electron the positively or the negatively charged particle? :facepalm:
17. Re: Your Mom's House by peragrin · 2013-09-16 11:14 · Score: 1
  
  No mass isn't the gravitational source by itself. There is another link between the two. Yes the higher the mass the higher the gravity. but this map shows you can get fluctuations in gravity's acceleration not only based on altitude as expected, but densities or other sources.
  As a mountain that is 7,000' shorter than everest has less gravitational pull. Look at that map. areas that are volcanic have greater gravitational pull.
  Something else is affected the expected numbers. density of the mantle is a good candidate.
  
  --
  i thought once I was found, but it was only a dream.
18. Re: Your Mom's House by Anonymous Coward · 2013-09-16 15:49 · Score: 0
  
  "but densities or other sources." and "density of the mantle is a good candidate."
  So in other words, mass is the gravitational source, it just comes down to the distribution...
19. Re: Your Mom's House by somersault · 2013-09-16 20:27 · Score: 1
  
  I'm still hoping for an anti-gravity cloak
  It could cause problems for you to not be attracted to the sun, or the centre of our galaxy, etc :D
  
  --
  which is totally what she said
this is just the first step. by nimbius · 2013-09-16 01:51 · Score: 4, Funny

the more challenging and involved effort will be the calculus of integrating this detailed graviton map into future "your mother is so fat" jokes.

--
Good people go to bed earlier.
1. Re:this is just the first step. by drinkypoo · 2013-09-16 03:30 · Score: 1
  
  the more challenging and involved effort will be the calculus of integrating this detailed graviton map into future "your mother is so fat" jokes.
  Your mother is so fat, she has a uniform gravitational field.
  
  --
  "You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
Of course it does by Anonymous Coward · 2013-09-16 01:55 · Score: 0

My wife was visiting.
Don't know their science by Daimanta · 2013-09-16 02:00 · Score: 2, Informative

From the article: That means a 100kg person weighs 700g more near the North Pole, where gravity is 9.83ms-2, than at Peru’s Nevado Huascaran summit, where gravity is 9.76ms-2.
They are implying that mass is a function of gravity. Everybody who has had the most basic fundamentals of physics knows that mass doesn't change, only weight(measured in newtons)

--
Knowledge is power. Knowledge shared is power lost.
1. Re:Don't know their science by RichMan · 2013-09-16 02:05 · Score: 3, Insightful
  
  Grocery stores "weigh" everything in grams. Grams might be mass but the general populace uses mass interchangeably with weight.
  Hmm, can we use the map to get global scale calibrations to a normal mass. It would seem to be unfair that the same amount of material might cost more or less in different places due to scale errors that measure weight and use it blindly as mass.
2. Re:Don't know their science by i+kan+reed · 2013-09-16 02:07 · Score: 2
  
  Secretly, regular people who live in SI countries don't use or understand Newtons unless they're scientists.
3. Re:Don't know their science by Anonymous Coward · 2013-09-16 02:09 · Score: 1
  
  Yep. I regularly tell people I weigh 885 Newtons
4. Re:Don't know their science by Anonymous Coward · 2013-09-16 02:19 · Score: 1
  
  Fig or strawberry?
5. Re:Don't know their science by Dunbal · 2013-09-16 02:26 · Score: 2
  
  No, they are implying that here on earth, scales measure weight not mass, and the unit for weight and mass is one and the same on this planet. Tell me who actually uses the Newton to express their weight, outside a physics/engineering context?
  
  --
  Seven puppies were harmed during the making of this post.
6. Re:Don't know their science by Anonymous Coward · 2013-09-16 02:29 · Score: 0
  
  Mixed berry.
7. Re:Don't know their science by sjwt · 2013-09-16 02:30 · Score: 1
  
  Its 2013, how many IPADs is that!
  The Newton is so 90's.
  
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  You have 5 Moderator Points!
  Which Helpless Linux zealot/MS basher do you want to mod down today?
8. Re:Don't know their science by Anonymous Coward · 2013-09-16 02:45 · Score: 0
  
  Usually scales are calibrated by putting an object of known mass on them and making sure they show the correct mass.
  Unless it's the type of scales where you compare with known masses anyway; those work independently of the local gravitation (as long as that differs substantially from zero, of course).
9. Re:Don't know their science by Kjella · 2013-09-16 02:51 · Score: 5, Interesting
  
  Hmm, can we use the map to get global scale calibrations to a normal mass. It would seem to be unfair that the same amount of material might cost more or less in different places due to scale errors that measure weight and use it blindly as mass.
  For weights that are comparing against a known mass there is no problem. The 1 kg of material you want to buy will always weigh the same as the 1 kg on the other side of the scale weight, no matter if it's 9.76 or 9.83 newtons on each side. So these "global scale calibrations" just involve transferring around known masses and has been done for centuries. The only way the scale would be off would be if one arm was on the North Pole and the other in Peru.
  
  --
  Live today, because you never know what tomorrow brings
10. Re:Don't know their science by Charliemopps · 2013-09-16 03:01 · Score: 1
  
  Yes, I'm immediately taking this map to my drug dealer. I've been wondering for years why he will only let me make buys on Easter island... now it's become rather clear that I'm being ripped off.
11. Re:Don't know their science by rwise2112 · 2013-09-16 03:12 · Score: 2
  
  From the article: That means a 100kg person weighs 700g more near the North Pole, where gravity is 9.83ms-2, than at Peru’s Nevado Huascaran summit, where gravity is 9.76ms-2.
  They are implying that mass is a function of gravity
  Not really. They specifically say "weighs", which is weight, not "masses".
  
  --
  
  "For every expert, there is an equal and opposite expert"
12. Re:Don't know their science by camperdave · 2013-09-16 03:22 · Score: 1
  
  You're supposed to use balance scales, not spring scales when measuring mass. With a balance scale, the force on the test mass and the force on the counterbalancing mass are the same, so it reads properly regardless of the strength of the gravitational pull.
  
  --
  When our name is on the back of your car, we're behind you all the way!
13. Re:Don't know their science by jalopezp · 2013-09-16 03:45 · Score: 2
  
  Actually, they are not. No one thinks mass depends on gravity. What the article actually says is:
  
  That means a 100kg person weighs 700g more near the North Pole
  Weighs 700g more. Weighs. They are merely saying that weight is a function of gravity, which is of course, true.
  You are confused by the units they are using. This is actually the kilogram-force, a non-SI unit of weight, which converts to about 9.8N or 2.2lb. Cool, no?
14. Re:Don't know their science by Bigby · 2013-09-16 03:50 · Score: 1
  
  How much of an effect does centripetal force play here? Gravity is the centripetal force at the equator that keeps people from flying off the earth due to their tangential velocity. So the perceived gravity on the equator should be less, right?
15. Re:Don't know their science by K.+S.+Kyosuke · 2013-09-16 04:16 · Score: 1
  
  You see, that's what you get when you measure mass AND force both in pounds. It took me some time to understand why Americans measure specific impulse of rocket fuels in "seconds" when I knew since high school that the actual unit is Ns/kg.
  
  --
  Ezekiel 23:20
16. Re:Don't know their science by Bengie · 2013-09-16 05:50 · Score: 1
  
  New scales will need GPS build in so they can use the new gravity map to determine how many grams something is.
  
  In other news, purchasing drugs in Peru and selling at the North Pole for profit! Someone has to keep those elves peppy.
17. Re:Don't know their science by synaptik · 2013-09-16 05:57 · Score: 1
  
  The gram is both a unit of mass, and a unit of weight. The intended meaning is dependent on context. This is why your bathroom scale will happily express your weight in either pounds or kilograms.
  
  --
  HSJ$$*&#^!#+++ATH0
  NO CARRIER
18. Re:Don't know their science by Anonymous Coward · 2013-09-16 08:48 · Score: 0
  
  How many oldtons is that? Or longtons, shorttons, ye olde tonnes?
19. Re:Don't know their science by ArsonSmith · 2013-09-16 10:00 · Score: 1
  
  but my scale is really really big. Spanning form west to east Venezuela.
  
  --
  Paying taxes to buy civilization is like paying a hooker to buy love.
20. Re:Don't know their science by JesseMcDonald · 2013-09-16 10:07 · Score: 1
  
  For weights that are comparing against a known mass there is no problem. The 1 kg of material you want to buy will always weigh the same as the 1 kg on the other side of the scale weight ...
  True, but not all scales work that way. Many use a spring or pressure sensor rather than comparing weights directly, and thus wouldn't take variations in the gravitational field into account. These scales would need to be calibrated against a known mass if they were used in a different location than they were manufactured in. (Of course, they probably needed to be calibrated anyway...)
  
  --
  "The state is that great fiction by which everyone tries to live at the expense of everyone else." - Bastiat
21. Re:Don't know their science by JesseMcDonald · 2013-09-16 10:27 · Score: 1
  
  That means a 100kg person weighs 700g more near the North Pole
  You are confused by the units they are using. This is actually the kilogram-force [wikipedia.org], a non-SI unit of weight...
  Anyone would be confused by their units. Even if they did mean to refer to the kilogram-force (why?) they still got it wrong. The shorthand for kilogram-force is "kgf" or "kp", not "kg" or "g". The article's "700g" is a measure of mass, not weight.
  Better: A 100.0kg person at the North Pole weighs the same as a 100.7kg person at Peru's Nevado Huascaran summit.
  
  --
  "The state is that great fiction by which everyone tries to live at the expense of everyone else." - Bastiat
22. Re:Don't know their science by AJWM · 2013-09-16 11:26 · Score: 1
  
  Seconds as a unit of Isp is nice because it tells you how many seconds of e.g. 1 lb force thrust you get for 1 lb mass of fuel. (Or conversely, how many pounds force you get from that 1 lb mass of fuel if you burn it all in one second.) It's a handy comparison number.
  Granted it's kind of an odd unit if you're trying to work out trajectories and mass ratios and delta-vees and such, but hey, it's not rocket science.
  Oh, wait...
  
  --
  -- Alastair
"most detailed" too strong a claim by Anonymous Coward · 2013-09-16 02:21 · Score: 0

The statement that this is the "most detailed ever" is likely false -- US intelligence agencies did this work during the cold war to improve inertial guidance systems of ICBMs. Although, a direct comparison of the data is likely impossible due to classification.
1. Re:"most detailed" too strong a claim by Voice+of+satan · 2013-09-16 03:16 · Score: 2
  
  Indeed,
  The US, the French and probably the Russians have their own classified gravity maps. Essential to improve inertial guidance of ICBMs so the ones launched by submarines match the precision of ground based ones. I had a colleague whose works on acoustics where classified by NATO. It means he was forbidden to publish his work. I Guess this hasn't changed a lot and that a too precise gravity map could not be released even today.
2. Re:"most detailed" too strong a claim by K.+S.+Kyosuke · 2013-09-16 04:13 · Score: 1
  
  Are you sure this wasn't to increase the precision of the sub navigation itself, as opposed to more precise calculations of missile trajectories? Despite the fact that the unevenness of the Earth's gravity field has to be taken into consideration to some extent, beyond certain spatial resolution, this becomes meaningless - the small local variations essentially cancel each other out in their perturbative influence on the trajectory as the missile is passing overhead at high velocity, and from a high altitude, observing the influence of these changes on the trajectory is difficult anyway (much like a set of point lights illuminating a distant object almost uniformly, as opposed to a closer one passing along the lights). What the gravity field does for you in a submarine, however, is the option to use high-resolution gravimetric maps and an on-board precise gravimeter as another feed for the navigational system to improve the precision of the navigation and to decrease the time drift of the combined feed, which is much more important for precise launches. Without this, the submerged sub would only have INS. (You won't catch the GPS signal underwater, and you can't rely on it anyway since the enemy could either jam it of somehow disable the network before the attack.)
  
  --
  Ezekiel 23:20
3. Re:"most detailed" too strong a claim by geogob · 2013-09-16 04:35 · Score: 1
  
  In absolute it may be innacurate, but it may still be the most detailed ever in the sens of published work available to the public. The publication / availability of information is a critical factor for scienctifc work.
  No scientific work is complete before it has been published and peer reviewed.
Ground Truth? by ka9dgx · 2013-09-16 02:26 · Score: 1

I wouldn't dare use this "map" for any serious purposes. It appears all they did was add the fine details from a topographic map to the rather low resolution results of other surveys. There's no high resolution direct measurement of gravity here.
Don't match by Anonymous Coward · 2013-09-16 02:41 · Score: 1

Why the two images in the post don't match?
no key or legend by Gravis+Zero · 2013-09-16 03:03 · Score: 2

it's great and all that they posted a pretty picture but they forgot to add a key or a legend of some kind. a color gradient scale with some kind of metric is the least they could do, even the weather channel knows that!
i'm sure the people who made this are the same damn kids that keep walking on my! </rant>

--
Anons need not reply. Questions end with a question mark.
1. Re:no key or legend by Anonymous Coward · 2013-09-16 03:18 · Score: 0
  
  Also, apparently there is no gravity over oceans...
2. Re:no key or legend by AdamHaun · 2013-09-16 04:23 · Score: 1
  
  They had a scale in the first article. You can probably make your own using the tool.
  
  --
  Visit the
3. Re:no key or legend by AJWM · 2013-09-16 11:28 · Score: 3, Informative
  
  Of course there isn't. That's why boats float.
  
  --
  -- Alastair
I wonder how many countries... by Anonymous Coward · 2013-09-16 03:19 · Score: 0

..."An Australian-German team of researchers has developed the most detailed map of gravitational variations ever, using satellite data, gravitational readings and small-scale topographical models. They say the data will help civil engineers and miners, and will be available for free online. .." ...would have charged for it?
This is really the way science should operate. 'Open-source' the findings and let entrepreneurs develop applications without patent fights...
Perhaps it would be a good idea to encourage such entrepreneurs to make a contribution to science projects if they find them useful....
torrent? by vagn · 2013-09-16 03:32 · Score: 1

It would be fun to play with this data.
Anyone have a torrent?
Sad by Anonymous Coward · 2013-09-16 03:40 · Score: 0

They fail grade school science as well.
Obvious improvement by Anonymous Coward · 2013-09-16 03:41 · Score: 0

would be to use a large-scale topographic model. Too bad the researchers don't understand scale.
Bah by K.+S.+Kyosuke · 2013-09-16 04:02 · Score: 1

"Gravitational fields vary because the Earth isn't perfectly spherical."
Uhm, not just that. Gravitational fields also vary because different places on Earth (or other bodies, for that matter) have materials with different density under them, forming so-called mascons.

--
Ezekiel 23:20
1. Re:Bah by Pseudonym · 2013-09-16 14:29 · Score: 1
  
  Also, the variation is measured relative to the reference ellipsoid rather than a sphere.
  Only Google Earth thinks that the reference shape for the Earth is a sphere. Unfortunately, everyone wants their systems to work with Google Earth, so everyone has basically copied the mistake. Lars is thus responsible for effectively undoing 400 years of geography.
  
  --
  sub f{($f)=@_;print"$f(q{$f});";}f(q{sub f{($f)=@_;print"$f(q{$f});";}f});
Best ever? by khb · 2013-09-16 04:21 · Score: 1

Folks who fly ICBM's need very accurate masscon (mass concentration) maps for guidance. So I'll bet that various governments militaries have more accurate maps. They do, after all, have a bevy of satellites whose orbit perturbations allow the computation of such things to any degree of accuracy desired ;>
Whether they make displays as nice, I don't know.
1. Re:Best ever? by GodfatherofSoul · 2013-09-16 04:52 · Score: 1
  
  Do people actually actively guide ICBMs? I'd figured they were completely automated. And, how accurate do you need to be with a nuke?
  
  --
  I swear to God...I swear to God! That is NOT how you treat your human!
2. Re:Best ever? by K.+S.+Kyosuke · 2013-09-16 04:59 · Score: 1
  
  I'd really like to see some numbers to support this claim. Just because mascons cause *measurable* changes in trajectory doesn't mean that the influence of any but the largest ones (or just large-ish, which sort of ruins the "very accurate maps" part) is such that it would outweigh the influence of the unguided atmospheric reentry on the actual CEP. And what about the constantly changing effects of the solar activity on the height of the atmospheric boundary itself? That's also one other variable you can't account for in advance that probably has a greater influence on the CEP than small-ish mascons, thus rendering their survey for purposes of increasing guidance precision meaningless.
  
  --
  Ezekiel 23:20
3. Re:Best ever? by AJWM · 2013-09-16 11:37 · Score: 1
  
  The more accurate you can make the nuke, the smaller it can be. Saves you nuclear materials and launch weight.
  And against hardened targets like missile silos or command bunkers, pretty accurate (eg, Cheyenne Mountain couldn't withstand a direct hit, but it could a nearby miss. Colorado Springs would be toast either way.)
  ICBMs are pretty much autonomous once launched (I would assume/hope they have an abort mode), but their targeting data is updated regularly (especially true for sub-launched missiles, of course, but also for the independently targeted warheads on a MIRV.)
  
  --
  -- Alastair
4. Re:Best ever? by AJWM · 2013-09-16 11:47 · Score: 1
  
  That's a reasonable point on the atmospheric effects of reentry, but that's only in the last couple of hundred miles, so any angular deflection will have a lower effect on the CEP than would even a smaller deflection closer to the launch. Over a few thousand miles, a slight angle change makes a big difference.
  And, you're assuming the reentry is unguided. That isn't necessarily the case. Even a simple cone can have some crossrange depending on the relation of center of mass vs center of aerodynamic pressure, with small thrusters, aerosurfaces, or weight-shifting to modify that. (Not that I know for sure one way or the other; if I did I probably couldn't say.)
  
  --
  -- Alastair
5. Re:Best ever? by turbidostato · 2013-09-16 13:33 · Score: 1
  
  "Folks who fly ICBM's need very accurate masscon (mass concentration) maps for guidance."
  Or what? The 10 Mt ICBM will boom 10 m out of its target on the other side of the world?
Hm, shouldn't one be heavier at high altitude? by Anonymous Coward · 2013-09-16 04:22 · Score: 0

Isn't gravity defined by the mass (gravitons anyone)? Going towards the centre of the Earth would render you weightless.
At the top of the mountain, should have a stronger gravitational pull. For example, on Jupiter being a bigger object, the gravitational pull is a lot stronger on its surface. So the more mass you have under your feet, the stronger the gravity.
1. Re:Hm, shouldn't one be heavier at high altitude? by K.+S.+Kyosuke · 2013-09-16 04:47 · Score: 1
  
  If by "heavy", you mean mass, then that is certainly the case: by working upwards in the conservative field, your mass increases towards an asymptote as you're removing the negative binding energy.
  
  --
  Ezekiel 23:20
ho hum... by vettemph · 2013-09-16 06:14 · Score: 1

maybe I'm not understanding the situation of the gravity here.

--
The government which is strong enough to protect you from everything is strong enough to take everything from you.
Islands have high gravity? by Anonymous Coward · 2013-09-16 06:45 · Score: 0

The map shows a lot of little islands in red. So islands have a higher gravity than than most other areas? And are on par with the tallest mountians? Even with less dense water surrounding the islands instead of land?
1. Re:Islands have high gravity? by spike+hay · 2013-09-16 09:26 · Score: 1
  
  From Newton, the gravitational potential from a point source is mass*G/distance. With topography, there are two things acting. Because mountains are high, they are further away from the Earth's center of mass (typically, the Earth's gravitational potential map is modeled as a multipole expansion of Legendre polynomials centered at point source at the center of the earth).
  However, there is also the gravity of the mountain(s) itself pulling you down. In most mountain ranges, there is lower gravity because of isostasy. The crust is floating on the mantle. Contintental crust is less dense than oceanic crust, and thicker. That is why it is higher than the floor of the ocean. It floats up more like a piece of styrofoam on water. Mountain ranges like the himalaya usually have thicker crust which displaces more of the upper mantle around it than thinner crust in places like Missouri. The crust in the Himalaya/Tibet is around 70 km thick, whereas normal continental crust is more like 30. Assuming close to isostatic equilibrium, from buoyancy the 70 km thick crust (averaging 5 km in elevation so 65 km below sea level) has roughly the same weight as 30 kilometer thick non-montane crust + 35 km of mantle.
  However, in the mountains, you are further away from the center of the earth, so there is less gravity.
  Seamounts are a different story. They are small, so instead of being in isostatic equilibrium the crust supports them like an elastic beam. They are also made out of heavy oceanic crust. That means they have high gravity because their mass isn't compensated. However, they do sink eventually. That is why if you look at the Hawaii/Emporer seamount chain, the Big Island is the newest and highest, while they get lower and eventually are no longer above sea level as you get older.
  
  --
  If you don't understand any of my sayings, come to me in private and I shall take you in my German mouth.
2. Re:Islands have high gravity? by spike+hay · 2013-09-16 09:48 · Score: 1
  
  Also, looking at the world map, it is a map of Bougeur anomalies (or using some other correction), which are gravitational anomalies corrected for the elevation they are taken at and the mass of the topography. That is why a good portion of mountainous areas are shown in red.
  The map of Australia is just straight-up gravity (and is different from Australia in the global anomaly map).
  
  --
  If you don't understand any of my sayings, come to me in private and I shall take you in my German mouth.