A Matter of Some Gravity

The BBC has a very well done article on the geoid as mapped by the GOCE satellite. A geoid is a surface of gravitational equipotential. Other ways to say the same thing would be that the force of gravity is the same at all points, or that an observer walking on that surface would feel no uphill or downhill- he might be able to see high places (farther from the Earth's center) or low places, but it would require the same amount of energy to walk "uphill" as down. A ball placed on the surface wouldn't roll.

The article does a good job of explaining that idea, how the data is gathered, and the uses to which it can be put. I'm delighted- and a little puzzled- by the high-frequency "waves" (which are even more pronounced in the full-size version at the link) in the image, but the article implies that they are real, and not some artifact of processing. Another mind-boggling bit of info is that the satellite has a precision of one part in 10^13! Geowhizzics amazes me.