Mapping the pull of gravity on Earth

This globe—the BBC has a spinnable version—shows you how the strength of gravitational pull differs in different places around the Earth. The yellow areas were where gravity is strongest. The blue spots is where it is weakest.

The picture you see here isn't meant to be a totally accurate representations, it's just meant to get across the simple idea of differences in gravity, separate from other planetary systems. The BBC describes the finished product as looking something like a potato.

Technically speaking, the model at the top of this page is what researchers refer to as a geoid. It is not the easiest of concepts to grasp, but essentially it describes the "level" surface on an idealised world.

If you were to place a ball anywhere on this potato, it would not roll because, from the ball's perspective, there is no "up" or "down" on the undulating surface. It is the shape the oceans would adopt if there were no winds, no currents and no tides. The differences have been magnified nearly 10,000 times to show up as they do in the new model.

Even so, a boat off the coast of Europe (bright yellow) can sit 180m "higher" than a boat in the middle of the Indian Ocean (deep blue) and still be on the same level plane. This is the trick gravity plays on Earth because the space rock on which we live is not a perfect sphere and its interior mass is not evenly distributed.

Maggie Koerth-Baker is the science editor at BoingBoing.net. She writes a monthly column for The New York Times Magazine and is the author of Before the Lights Go Out, a book about electricity, infrastructure, and the future of energy. You can find Maggie on Twitter and Facebook.

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MattF

… and I should add that your GPS gizmo may be lying to you on this subject– raw GPS altitude data is altitude above the ‘ellipsoid’, a fictional ideal surface that does not contain the geoid correction. The altitude that GPS user sees may or may not include the geoid correction.
weatherman

Does this geodata make my ass look fat?
Pope Ratzo

So if I wanted to live where gravity was the weakest, where would that be?

I mean on Earth…
Anonymous

I’m not getting the “separate from other planetary systems” part. What is that supposed to even mean? The effect of gravity from other planetary systems is so incredibly weak that it’s completely negligible anyway. Also: “the yellow areas *were*” …? “a totally accurate representationS”…?

That morning coffee was decaf, yes?
BB

I think that gravity is stronger on certain days, as demonstrated by my inability to keep objects from being pulled to the ground. At least that’s my story, and I’m sticking with it.
staba

The things get interesting with global warming: The main reason for the big pull at Europe is the ice on Greenland. If that melts, the pull will decrease, hence the sea level declines as well.
Kaleberg

I was involved with a group that had done a similar visualization in the late 1980s using a similar dataset from the Seasat satellite. I pulled the old VHS tape and put it on Youtube at: http://www.youtube.com/watch?v=oAxwt-09h8g

It’s the same old Earth. I have no idea of where the dataset is. My guess would be a moldy 9 track tape somewhere between the Ark of the Covenant and Citizen Kane’s sled.
francoisroux

Just thinking out loud, shouldn’t the sports results for disciplines like the high jump and weight lifting perhaps be adjusted accordingly?

Talk about open a can of worms…
Anonymous

is this part of the new valve ARG too?
jpgsawyer

Is it me or does 180m seem to high? Is there a units issue in the original BBC article.

I tried to see if there was a scale on the GOCE data on their website and failed.

Any one else see something I missed?
cella

This is why I have put on weight since moving to Europe.
irksome

Still, it looks painful.
Anonymous

So, are they trying to say that Americans and Canadians weigh less than the rest of the world?
millrick

also
http://www.guardian.co.uk/science/2011/mar/31/goce-maps-earth-gravity
and
http://www.scientificamerican.com/blog/post.cfm?id=the-geoid-why-a-map-of-earths-gravi-2011-04-01
Mister44

It looks like God’s stress ball after listening to Charlie Sheen.
millrick

i hereby designate this globe the Play-Dohâ„¢ Earth.

–
BBC’s animation is better than the Guardian’s or S.A.’s, IMHO
Anonymous

So is the Earth actually potato shaped, or does the model simply represent the variances in gravity. With the only way to quantify it to the human eye is to show it’s imbalance via, a non-global shape?
Anonymous

There seems to be a superficial correlation between this and the world map of penis sizes.

http://boingboing.net/submit/2011/03/world-map-of-average-penis-size.html

Just sayin.

Robby Staven
Latente

buy gold in brasil
sell gold in england

:infinete money:
MattF

Sorry, but your description of the geoid as a surface showing where Earth’s gravitational force is ‘stronger’ or ‘weaker’ is just wrong. Earth’s gravitational potential is equal everywhere on the geoid. Whether the gravitational force is stronger or weaker depends on the gradient of the potential, which is not shown.

The easiest (IMO) way of thinking about the geoid is that it shows the correct generalization of the notion of ‘sea level’ when you are on dry land. So, when your GPS gizmo shows you an altitude of, say 100m above sea level when you are driving on Route 95, it is telling you that your distance above the geoid is 100m.