Earth: Not as Round as I Thought.


Apparently that’s what the earth’s surface would look like if there were no tides or currents. Not as spherical as I thought. Naturally we should expect a bulge toward the equator since the Earth rotates, but there’s not as much radial symmetry as I’d imagined. Source

I was a little shocked at how non-ellipsoid the geoid is, so I finally looked it up on Wikipedia:

the geoid is by definition a surface to which the force of gravity is everywhere perpendicular

Pretty straightforward. The point about how the ocean would be if there were no currents is more or less irrelevant. I guess any small change in the surface of the Earth wouldn’t greatly affect the plumb line. It’s also possible that the geoid surface will submerge below actual continents or even ocean floor - the plumb line dictates it. That dented upper left portion in the image must feel like a local hill, gravitationally, when you go over it - that is, I don’t think you can take any image of Earth from space, that has this apparent dented shape (and it’s not just the ocean and atmosphere rounding things out).