Monday, May 14, 2007

Shape of the Earth

One of the very stupid things you learn in school is about the shape of the Earth. You are told that the Earth is not exactly spherical - it has a "geoid" shape (which basically means it has a shape like the Earth... very intelligent). Like in the Microsoft joke, this is technically true, but rather pointless. The Earth's radius is 6500km; the deepest trench in the ocean is 11km and the highest mountain is almost 9km. Which makes it a pretty damn good sphere, with a precision of about 1:600.

Think about it this way: the same precision on a billiard ball with a radius of 3cm would mean a maximum error of 0.05mm, or 50 microns. I'd call that a perfect sphere...

2 comments:

Bertrand Le Roy said...

Ah, you are wrong, but not by much. Yes, it's a pretty good sphere, but it's not the ocean trenches and mountains that make up for the biggest imperfection, it's the deformation due to its rotation, as postulated by Newton and verified with greater and greater precision over the years (yeah, one more good reason to think it's the Earth that rotates and the Sun only appears to do so ;) ). That difference is about 43 kilometers, a little more than what you state here, but not that much. So yeah, it's a good approximation of a sphere.

Marcel said...

I knew about the deformation of the Earth, I just believed it was 28 km. As for it being caused by the Earth's rotation... that is not the only explanation. (A much stronger "counter" to the geocentric position is the existence of geostationary satellites; the same mechanism explains both.)