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Earth Smaller than previously thought

http://www.cosmosmagazine.com/node/1428

Look the diameter is now 12,756.274 km.

These amazing researchers claim that such a difference is "really" important. It is vital to know to the exact mm what the diameter of the earth is.

Looking out my window right now I can see the bottom of the bay (the tide is going out). On the other side of the bay, I see the exposed part of the bay that was completely covered when I arrived this morning. Guesstimating, right now the difference is about 2m. Up above that is the hill that is at least 20m. There are on top of that, blocking my view of Mt Rainier, which is 4392m.

Could someone smarter than me explain how it is possible that someone educated in a scientific university could get excited about 5/12,756,274,000. ...

Oh wait.. We know that we can detect substances at the ppb threshhold so measurements out to 12 significant digits are really possible.

Jeb can probably answer this question better, but I think this is another example of the new elite smoking crack and paying way too much attention to their calculators that happily display 20 digits.

When I took Integral Calculus, our teacher, a TA, instructed the class to NOT use a calculator when taking the test. It made his job a pain in the ass when someone would type 3.1415927 into their calculator for an interim step of a calculation. Of the 30 people in the class, maybe 3 actually listened to him. We did it because we noticed that usually, those irrational numbers ended up disappearing. The majority of the class didn't get it. If he had been a little brighter, the teacher could have fixed this problem in a heartbeat.. "Anyone using their calculator to explicitly calculate Pi, e, or any other irrational number will have their answers marked as incorrect." The teacher didn't want to fail them for not following this particular direction though, especially if they were getting the concepts correctly. I think those people who were addicted to their calculators are the ones making these pronouncements.

Re: Earth Smaller than previously thought

Brad, you are missing the point. The time to measure the diameter of the earth to greater and greater precision is over. As you say, who cares for that last mm? Why, the people who measure it, they care. Their problem is where do they get the fund\$ for their re\$earch? If you submit a proposal to measure the diameter of the earth to the nearest tenth of a mm, no responsible agency, public or private, is going to fund it. So, what to do?

Well, you go to irresponsible agencies, those that will fund anything that has the slightest relationship with global warming. Now if you were heading such an agency, would you not fund this?

"A proposal to determine the effect of global warming on the diameter of the earth"

Now they will have the funding to go to the nearest hundredth of a mm.

Re: Re: Earth Smaller than previously thought

Oh dear, what a lot of nasty cynics we have become! Brad & Jaime are both correct of course as far as the AGW aspect Is concerned, but as a surveyor there really Is an important aspect to it.
As the lad said in the article, if we can't place the size of the earth to the mm, we can't place the satellites to the mm and can't measure things on earth to the mm. What we are actually measuring isn't the size of the earth - as Brad implied, radius to where on the earth? Geodesists are a strange breed, and the earth Is neither a sphere (which will do for crude calculations, like how far Is London to Sydney in air miles) nor a regular spheroid (which most of us use for calculatiuons for mapping). What Is used for satellite navigation Is an equally ficticious body called the Geoid, which Is a lumpy, 'orrible object on which only a geodesist would wish to calculate. This (very roughly) Is the shape of an earth covered with water with no tides and Is used to construct a gravitational model which Is used to predict satellite orbits and thus allow their distance measurements to be related to a real shape. This does allow you to measure tidal heights out at sea with precision and to get a good idea of overall sea levels.
All of which Is of no use whatsoever to a True Believer, since we only have satellite-based sea level measurements going back about 20 years. Everything before that was measured on tide gauges related to land levelling datums which were determined from tide gauge records determining Mean Sea Level.(!) Given that the "solid" Earth bounces about like a W's Ds (yes there are earth tides of about a foot in some places) and many of the northern (=oldest) tidal records are in areas where the land Is still rebounding after the last glaciation and all over the globe sea level has risen, pressing down on the oceanic crust and causing the land to rise, anyone (even the Proudman Lab.) who tells you that sea level rise has been measured to centimetric accuracy over the last century Is talking b******s.

Re: Earth Smaller than previously thought

I'm puzzled.

The headline says that Earth is SMALLER but the article seems to suggest the diamter is LARGER.

Quote:

"German scientists from the University of Bonn took part in an international project to measure the diameter of the world and came up with the 5 mm increase."

Hmm.

Does that change the globe's surface (and therefore the energy absorbtion per square meter) calculation?

Should we assume that the diameter is constantly changing? If it is, how does that affect our most 'precise' measurements?

What effect does continetly drift of 18mm per year have on the volume and heat transport potential for the North Atlantic and the areas that are proving the extra water volume as the movement suck in vast quantities of water to fill the gap?

If D= approx 5, pi x D = close to 18

Could these numbers be connected?

Fianlly, how many fairies can you fit on a pinhead at the bottom of my garden?

Grant

PS, bit at least I now know why my GPS system is not always in agreement with my actual position - well, unless the maps are wrong I suppose.

Re: Re: Earth Smaller than previously thought

Yep, your maps are wrong - or not, depending on what you want. If your GPS doesn't agree, have you checked it's set to the same datum as the map? (Believe me, this can get horribly complicated)

"What effect does continetly drift of 18mm per year have on the volume and heat transport potential for the North Atlantic and the areas that are proving the extra water volume as the movement suck in vast quantities of water to fill the gap?" Very little, as the continents are essentially sliding about over the mantle, so as the Atlantic grows, the Pacific shrinks. On the other hand, if anyone tells you he can measure it - he's lying.

Re: Re: Re: Earth Smaller than previously thought

Jerry,

That GPS is stuff is just too complicated.

I mean I really need to know whether I have just parked on the pavement rather than the road. A few on-screen pixels either way could be the difference between success and failure and therefore influence whether I am awarded some sort of official penalty.

Likewise if I stop to investigate strange bumpiness it would be good to know whether or not I am on a level-crossing. ust two examples where I am convinced in my believe that millimeters make a difference.

And I don't think you shoudl dismiss the movement of masses of water so lightly. After all if the void in the middle of the Atlantic is filled from the Pacific, especially if it comes through the Panama Canal, it will be adding warm water to the Gulf Stream whereas if it is stuff sneaking in from the Arctic (or maybe the Greenland Ice Sheet) it will be cold. Clearly there would be different effects on UK weather. I think we should be told.

Grant

Re: Re: Re: Re: Earth Smaller than previously thought

You're not getting anything like centimetric precision out of your GPS. I'm currently sitting on a rig we've just moved and are getting +/- 25cm standard deviations with several thousand quid's-worth of kit. Even so, it boggles the mind what we can get for a couple of hundred or so.
If the Pacific gets into the Atlantic via the Panama canal it's doing bloody well - from what I recall it rises a couple of hundred feet or so in the middle. Far easier to go round Cape Horn.

"Clearly there would be different effects on UK weather. I think we should be told."

But we are told! The trouble is, ungrateful s*ds that we are, we don't believe them and demand evidence instead of thundering edicts from on high.

Re: Re: Re: Re: Re: Earth Smaller than previously thought

"I'm currently sitting on a rig we've just moved and are getting +/- 25cm standard deviations with several thousand quid's-worth of kit."

Jerry,

Going off the prime topic somewhat, here is a reference to a system that claims it provide a 40cm accuracy for fast moving vehicles. For an upgrade they suggest that the top of the range device can get 2cm accuracy.

now this kit is also likely to cost, in total, a few grand. If the costs were, for the sake of argument, the same, would the 2cm accuracy be imorotant enough to force a change of system?

If this system was twice the cost of your existing system, would it be worth changing?

Etc., etc.

Just interested in gauging how important these things are in a cost/benefit calculation.

Grant

Re: Re: Re: Re: Re: Re: Earth Smaller than previously thought

Grant,
Yes, but don't believe everything a seller tells you. At that sort of level all sorts of things become important (like choice of geodetic datum, sunspot activity, reference system, etc.). Standalone GPS now gives an accuracy of about +/- 5-10m over most of the useful parts of the globe, with a Wide Area Differential setup you can be down to about half a metre and with RTK you can get *relative* accuracy of about 5mm. No sane person wants to do that!

Re: Re: Re: Re: Re: Re: Re: Earth Smaller than previously thought

Jerry,

"... and with RTK you can get *relative* accuracy of about 5mm. No sane person wants to do that!"

Agreed for normal use, but there are a few applications where such levels of accuracy might be considered important enough to make use of the technology.

Automotive testing and in particular racing where the practitioners are looking for differences of 1.10th of a second or less and a 'more' accurate positional plot might help the analysis are examples. I doubt that better than half a meter is required in, say, agriculture when ploughing a field.

Also there seem to be a lot of insane people around these days. So I would imagine demand (or maybe desire even if budget is absent) might be higher than one might think.

So when positioning a rig is there no advantage to having accuracy greater than 25cm? (I ask even though I cannot imagine that it would be realistically possible to be much more accurate than that with what I assume is a large structure at sea - have I guessed wrong? That said I recently visited the Kennedy Space Centre and the degree of positioning accuracy (not gps) required for the shuttle/orbiter combination to be put together (according to the tour guide's information) was difficult to comprehend.

Grant

Re: Earth Smaller than previously thought

Let me put forth a slightly analogy.

The Tacoma Narrows bridge is getting a big brother. The two "expansion" joints were recently put in place. There was some hubbub over these two critical pieces of the bridge because no one bothered to talk to the Department Of Transportation about them. They were bigger than the roads would allow to be transported. A truly exciting example of the fact that every project seems to miss some important element.

The key though is Expansion and Contraction. I suppose if you were able to freeze the earth to a moment in time, you might be able to calculate the diameter to some degree of precision, but diameter of the earth probably varies by more than the change.

Of course this doesn't keep 30 people employed.

I do see another "Day after Tomorrow" plot here though:

A group of dedicated scientist measuring the earths diameter discover that the earth is expanding(contracting) at such a rate that the force of gravity is decreasing (increasing) such that the atmosphere will begin to expand and get lost ( or contract and compress). We will all then be suffocated (or burned up). Nicholas Cage will make a heroic attempt to squeeze the globe together by detonating 30 nuclear devices equidistant around the planet to recompress the planet (place in the core to cause the planet to reexpand).

Dramatic music.