- Our planet isn't merely not regular in shape, it's not even regularly irregular!
- The Earth's shape is usually approximated with an ellipsoid, or the volume described by rotating an ellipse about an axis in space
- Ellipsoidal parameters include:
- Semi-major axis (equatorial radius ~ 6,378km in GRS80)
- Semi-minor axis (polar radius ~ 6,356km in GRS80)
- Flattening ( (major - minor) / major )
- Eccentricity (deformation from spherical shape)
- The science of estimating and measuring the Earth's shape is called geodesy
- Ellipsoid differs from geoid, an empirical model of the Earth's surface based on gravity measurement
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