Wednesday, October 31, 2018

[ezkbrgps] Shape of the Earth and the definition of the meter

The meridional circumference (polar circumference) of the Earth is 40007 km, 40008 km, or 40009 km, depending on the source.  (Why is there a discrepancy?)  The fact that it is so close to 40000 is not a coincidence: the kilometer used to be defined as 1/10000 the distance from north pole to equator.

What is the reason for the roughly 8 km difference from 40000?  Was it lack of precision in measuring the Earth back in the day?  Or more intriguingly, is it caused by the Earth not being a perfect oblate ellipsoid?  Perhaps going the rest of the way around is a bit longer than symmetry predicts (pear-shaped), or it depends on what meridian you measure along (triaxiality).

No comments :