Mapping the pull of gravity on Earth

By Maggie Koerth-Baker at 5:27 am Monday, Apr 4

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.